| Chinese fir (Cunninghamia Lanceolata) is the unique important fast-growing timber species in southern China. With the growing planting area of Chinese fir, broadleaved forests area reduced sharply, more and more Chinese fir planted continuously at the same ground, which caused a decline in plantation productivity, so that the arisen "second generation effect" of plantation management had a serious impact on the continued operation of Chinese fir plantation. A large area of the fast growing Chinese fir forest has built during the 1960s and 1970s in southern China forests, most of which have entered into the final cutting stage and all faced with the problem of second-generation update. Thus settlement of soil degradation caused by second- generation update of large area Chinese fir plantation in the South has become the major subject,which starve for solution in the current forestry production. At present, prevention and control measures of soil degradation in Chinese fir plantation mainly promote the growth of Chinese fir through the improvement of soil conditions.This traditional control methods of changing land with trees are with little regard for the efficiency of nutrient use by selecting the high forest trees to adapt to the soil conditions to study, especially efficient use of nutrition genotypes are rarely researched to gain high yields at the lower level of fertility in forest land. The current fast-growing genotypes of forest trees is not necessarily the highest in nutrient use efficiency, some get high yield at the expense of the nutrients in forest land. Although this genotypes grow fast, the consumption of land fertility is very high. Thus control effect on land capability decline of plantation was not obvious up till now, and it has not yet been developed effective measures to control productivity decline of continuous plantation for the production of large-scale application. How to solve the reforestation of large-scale plantation of degraded soil has now become the major issue urgent to resolve in forestry production.This paper is based on the characteristics with low available phosphorus but rich in total phosphorus in southern forest soil, and set about improving the efficiency of the use of phosphorus of forest lands in fir through comprehensive investigation and study of growth of test stands of offspring of Chinese fir clones in different areas of different age determination and nutritional characteristics in Center of China fir. The P efficient utilization of fast-growing Chinese fir clones were initially screened out by analysis of P use efficiency in different productivity of the offspring test stands of Chinese fir clones. Through indoor simulation experiments of homogeneity and heterogeneity for the phosphorus, adaptation to physiological and biochemical differences of different low-phosphorus stress in different Chinese fir clones were analyzed and determined, then Chinese fir clones of P use efficiency were selected by increasing activation of insoluble phosphate in soil and enhancing phosphate starvation resistance, and specific indexes of P efficiency in different Chinese fir clones were pointed out, thus the internal mechanism that adapted to low-phosphorus stress with efficient utilization of P in fast-growing Chinese fir clones were clarified, ecological genetic traits of tolerance to low phosphorus nutrition of Chinese fir were revealed, so all of which provided a theoretical basis to improve the theory and methods of forest nutritional genetics; Germplasm resources of tolerance to low phosphorus of Chinese fir were developed for the promotion of production applications, which provided a new way to control the decline in continuous productivity of Chinese fir plantation. Its application prospects are extensive, and economic, ecological and social benefits are extremely significant. Main results in this paper:1,There were significant differences in growth of progeny test plantations of the 84 different Chinese fir clones with 7a year-old. The average annual growth of tree heights,diameters at breast height and volumes of the progeny test plantations of different Chinese fir clones were 0.84 m·a-1,1.12 cm·a-1,0.0036 m3·a-1 respectively. M8, M10, M11, M23, M28, M29, M30, M32, M33, M34, M101, M102, M136, M151, M211, M239 and M249, etc 17 fast-growing Chinese fir clones were initially screened out, which accounted for 19.77 % of the total number of the tested clones.2,There were significant differences in growth of progeny test plantations of the 45 different Chinese fir clones with 17a year-old. The average annual growth of tree heights,diameters at breast height and volumes of the progeny test plantations of different Chinese fir clones were0.94 m·a-1,1.22 cm·a-1,0.0161 m3·a-1 respectively. M17, M34, M35, M40 and M43 clones were initially screened out, which accounted for 11.11 % of the total number of the tested clones. Compared with the control 1, the average realistic genetic gains of tree heights, diameters at breast height and individual volumes in 17 clones mentioned above were 11.81 %,15.50 % and 37.16 %.3,The average of PUE of whole tree of different Chinese fir clones with 17a year-old was 4886.67 g·g-1. Among them, PUE of whole tree was highest in M1 Chinese fir clones, which was 1.27 times of the average. Then these efficiencies were in ascending order as follows: M17>M10>M9>M45>M23>M41>M3>M19>M24>M43>M8>M25>M37>M34.PUE of stem in different clones for sequencing were: M1>M10>M9>M17>M41>M23>M19>M45>M3>M43>M8>M25>M24>M37>M34, among them, M1 was 25.84 % more than the average, which was 1.57 times of M34.4,Different treatments of P had remarked difference on roots growth of Chinese fir clones. In rich insoluble Fe-P treatment of P1, the averages of root length, surface areas, average diameters and volumes in different Chinese fir clones were 15.58 m, 566.56 cm2, 0.77 mm and 17.13 cm3 respectively. Among them, roots in M8, M9, M11, M39 and M302 grew well, which showed that foraging ability in this 7 Chinese fir clones was stronger in the adversity of absence of available phosphorus but rich in insoluble iron and phosphorus. In P-deficiency treatment of P0, roots in M1, M3, M9, M17, M21and M302 grew well, which noted that the four Chinese fir clones had a ability of P-deficient resistance. 5,Different P treatments had remarked difference on biomass increment of Chinese fir clones. Compared with the normal phosphorus supply treatment P2, the biomass of different Chinese fir clones by 24.06 % on average in sufficient insoluble phosphate conditions in treatment P1 .Among them, increase amplitude of M302, M9, M8, M1, M11, M17, M39 and M19 were, respectively, 7.65 times, 6.23 times, 5.93 times, 4.25 times, 1.98 times, 1.84 times, 1.45 times, and 1.25 times of the average of increased percentage. It was obvious that foraging ability in this eight Chinese fir clones was stronger in the absence of available phosphorus but insoluble iron and phosphorus sufficient adversity; In P-deficiency treatment P0, biomass in different Chinese fir clones decreased by 31.97 % on average. Among them, P-deficient resistance ability was larger in M39, M1 and M302, maintaining a high productivity, and the increase in the percentage were respectively 96.17 %, 32.60 % and 26.36 % compared with that in treatment P2, which may be related to the higher phosphorus use efficiency in their body; Productivity of other tested clones was significantly influenced by P-deficient stress, and added biomass increments were smaller than that in treatment P2.6,Different treatments of P had different impact on accumulation and distribution of P in different Chinese fir clones. The average of P content in different organs of tested 21 different Chinese fir clones showed in the order of size: leaves> roots> stems. Content of P in roots was impacted significant on low-phosphorus stress, which might be caused by those: when Chinese fir clones encountered low-phosphorus stress, On the one hand, P in plants transferred to underground portion to improve the productivity of roots to enhance the foraging ability of P in soil, on the other hand, roots activated insoluble phosphate in soil so that P content of the roots increased. In treatment of P1, P content in M5, M17, M19, M21, M24, M37, M41, M48 and M302 Chinese fir clones was higher; In treatment of P0, P Content in roots of M3, M4, M5, M19, M21, M24, M28, M39, M102 and M302 Chinese fir clones was higher.7,Different treatments of P had different impact on P use efficiency of Chinese fir clones. In treatments of P2, P1 and P0, average of PUE in tested 21 different Chinese fir clones were 1.826 kg·g-1, 1.663 kg·g-1 and 1.814 kg·g-1 respectively, which further indicated that Chinese fir clones might decrease PUE mainly through activated absorption of the roots of insoluble iron phosphorus, and speeding up P recycling and reusing at the same time in the adversity of lack of available phosphorus but rich in total phosphorus; In treatment of P1, PUE in M3, M4, M19 and M38 Chinese fir clones was larger than that in treatment of P2, and the increase amplitude was 2.48 % 28.04 %; In treatment of P0, PUE in M41, M1, M19, M9, M17, M11, M37, M24, M21 and M211 Chinese fir clones was all larger than that in treatment of P2, and the increase percentage was declined by 1.49 % 34.94 %.8,With the low-phosphorus stress increasing, Chlorophyll in leaves of Chinese fir decreased sooner, which showed Chlorophyll was more seriously damaged. In normal phosphorus supplied treatment of P2, as test time prolonged, average of total chlorophyll in different Chinese fir clones showed the trend that it rapidly increased firstly and then slowly increased; It showed the same law change in the treatment of P1. In treatment of P0, the total amount of chlorophyll increased rapidly at first, then rate of increase slowed down later, and decreased finally. In the end of the treatment of P1, the increase amplitude of total chlorophyll of M3, M18, M24 and M102 Chinese fir clones was larger than that in treatment of P2. In the end stress treatment of P0, only the increase amplitude of total chlorophyll of M5, M18 and M41 Chinese fir clones chlorophyll was larger than that in treatment of P2.9,The more serious low-phosphorus stress was, the faster increased MDA content in leaves of Chinese fir. With the extension of test time, in the normal phosphorus supplied treatment of P2 ,the average MDA content in leaves of different Chinese fir clones showed such trend :it was declined slowly firstly, and then decreased substantially, finally it was slowly increased; Change law in treatment of P1 was similar to that in treatment of P2; It showed different change law in treatment of P0: there was a slow rise firstly, and then a sharp decline, finally a slow increase. Compared with the end of treatment of P2, increase amplitude of MDA content in leaves of M4, M19, M39, M102, M211 and M302 Chinese fir clones was smaller in treatment of P1. While increase amplitude of MDA content in leaves of M4, M5, M11, M18, M37, M38, M48 and M211 was smaller in treatment of P0.10,With the stretch of test time, soluble protein content in leaves of Chinese fir clones showed similar law changes in different treatments of P: increase→decrease→slow down to the level of stress before. However, the change law of soluble protein content in leaves of Chinese fir clones was widely different. Compared with the increase amplitude of soluble protein content in leaves of Chinese fir clones in the normal phosphorus supplied treatment of P2, the increase amplitudes of M1, M3, M4, M8, M18, M19, M24, M28, M37, M38, M48 and M211 were larger in the primary stress treatment of P1, which showed that these 12 clones were more sensitive to the low-phosphorus stress. This might be due to that they could start the biological synthesis of enzymes and active substances of stress-tolerant protein in plants rapidly. At the end of stress, the increase amplitudes of M11, M18, M19, M37, M38 and M211 Chinese fir clones was larger, which might because that ability to activate insoluble iron in these six Chinese fir was larger in stress treatment of P1.This effectively alleviated the blocked plight of the normal protein synthesis in plants and improved the ability to synthesis of stress-tolerant protein. In the P-deficiency treatment of P0 at the primary stress stage, the increase amplitude of M1, M3, M4, M8, M9, M11, M19, M21, M24, M28, M38, M39, M41, M48 and M211 was larger. At the end of stress, the increase amplitude of M3, M4, M11, M18, M19, M21, M24, M38, M39 and M211 were larger.11,With the stretch of test time, law change of the average of APA activity in leaves of Chinese fir clones in treatment of P1 and P0 was similar to the treatment of P2: decrease slowly→increase→dropped to a lower level. However, the change law of APA activity in leaves of different phosphorus efficiency of Chinese fir clones was significantly different. The primary stress stage in treatment of P1, increase amplitude of APA activity in leaves of M1, M8, M9, M11, M17, M19, M39, M48 and M211 Chinese fir clones in tested 21 Chinese fir clones was larger than that in treatment of P2; In the end of stress, the increase amplitude of M3, M5, M8, M9, M11, M18, M19, M24, M28, M37, M38, M39 and M211 Chinese fir clones was larger than that in treatment of P2.In primary low-phosphorus stress of treatment of P0, increase amplitude in APA activity in leaves of M1, M8, M38, M41 and M211 Chinese fir clones than that in normal P supplied treatment of P2; At the end of stress, increase amplitude of M1, M3, M5, M8, M18, M19, M24, M28, M37, M39, M102, M211 and M302 Chinese fir clones was larger than that in treatment of P2.12,In different treatments of P, correlation between dry matter accumulation of Chinese fir clones and different physiological indicators was not very strong, but different morphological indicators of Chinese fir clones had more visible impact on dry matter yield. In normal phosphorus supplied treatment of P2, the correlation coefficient of the increment of root length, root surface area, root diameter and root volume of Chinese fir clones and the content of dry matter accumulation were 0.451, 0.544, 0.526 and 0.561, respectively; while the correlation coefficient were respectively 0.640, 0.686, 0.682 and 0.658 in adequate iron phosphate treatment of P1, P value test all showed significant correlation; Under phosphorus deficiency treatment of P0, root length, root area and root volume had significant impact on the dry matter yield, seedling height was also one of the decisive factor related to dry matter accumulation.13,The study in this paper found: M39 Chinese fir clones showed strong adaptability and maintained a relatively high rate of biomass accumulation under the environment that la对照of available phosphorus but rich in total P. Use efficiency of M39 Chinese fir clones that belonged to fast-growing Chinese fir genotypes of efficient use of P was also higher; While PUE of M3, M4, M18, M19 and M38 were higher but their biomass production were lower, M1, M8, M9, M11, M17 and M302 had fast-growing and high-yield features, but relatively low PUE. It was noted that the 11 Chinese fir clones had great potential of development, which was proposed to strengthen the improvement of research.From P-deficiency experiment of P0, this paper drew: characteristic of phosphate starvation resistance was obvious in M1 Chinese fir clones. In extreme adversity of P-deficiency, M1 Chinese fir clones could maintain a higher rate of root growth and dry matter accumulation, so it could be used as preferred material for genetic research of nutrition of Chinese fir; PUE in M9 Chinese fir clones was higher in completely P-deficiency adversity, but there was faster rate of root growth and a smaller biological accumulation. This may be related to that expanding foraging ability of the roots was higher, but the ability to reuse and transfer P in plants was poor.14,Different heterogeneity of phosphorus supplied treatment had obvious differences of impacts on root growth of M1 and M4 Chinese fir clones. There is little difference in roots growth between 2 pots of M1 and M4 Chinese fir clones were not large. In treatments of P2, P1 and P0, increments in these four indicators of root length, surface area, mean diameter and volume in rootâ… of M1 and M4 Chinese fir clones were all larger than those in root. But with the reduction of total phosphorus in growth medium, increments of four roots growth indicators of M1 Chinese fir clones showed some increase in the trend, which might be that it could adapt to low phosphorus stress through reasonable distribution of phosphorus in plants; While the roots of M4 Chinese fir clones in the growth medium containing insoluble Fe-P grew more slowly than those in lack of total P medium, which might be related to its activation ability of the Fe-P, if phosphorus were sufficient in plants, the ability of foraging through the extension of roots weakened.15,Heterogeneity of different P treatments had different impact on distribution of P in M1 and M4 Chinese fir clones. Differences of P content between root and stem in M1 Chinese fir clones under the normal phosphorus supplied treatment of P3 were smallest, while it had most obvious difference in P-deficiency treatment of P0; As low-phosphorus stress increased, differences in P content in roots and leaves had a descending trend. Compared with P content between rootsâ… and rootsâ…¡of M1Chinese fir clones, in two pots of normal phosphorus supplied treatment of P3, the difference of P content between rootâ… and rootâ…¡was 0.07g·kg-1; In treatments of P2, P1 and P0, P content in rootsâ… were respectively 0.18g·kg-1, 0.11g·kg-1 and 0.35g·kg-1 larger than those in rootsâ…¡, in which two pots of treatment of P0 had the largest differences in root P content. It noted that phosphate starvation-resistant M1 Chinese fir clones could maintain normal root growth through changes in distribution pattern of phosphorus in roots Chinese fir in adversity of extremely short of phosphorus in soil.The average of P content in roots of M4 Chinese fir clones were, respectively, 0.36 g·kg-1, 0.12 g·kg-1, 0.48 g·kg-1 and 0.10 g·kg-1 smaller than those in leaves in treatments of P3, P2, P1 and P0. Compared with P content between roots and leaves, in different treatments of P, differences were smallest in treatment of P0, while difference between the two was larger in treatment of P1. Compared with P content between rootsâ… and rootsâ…¡of M4 Chinese fir clones, difference of P content between rootsâ… and rootsâ…¡was small by only 0.04 g·kg-1 in treatment of P3; In treatments of P2, P1 and P0, P Content in rootsâ… were 0.11g·kg-1,0.01g·kg-1 and 0.04g·kg-1 larger than those in rootsâ…¡respectively, which showed that difference of P content in roots in two pot was largest in treatment of P2.And it showed that it had a strong activation capacity of iron-phosphorus and greater phosphorus content in roots of Chinese fir clones, in the adversity of lack of available phosphorus but rich in total phosphorus in soil.16,Heterogeneity of different P supplied treatments had obvious impact on PUE of M1 and M4 Chinese fir clones. With the increasing stress of Fe-P, PUE of M1 Chinese fir clones had a gradually increasing trend. Compared to normal phosphorus supplied treatment of P3, PUE reduced by 21.20 % and 2.94 % respectively in treatments of P2 and P1, while increased 7.78 % in treatment of P0, which noted that the less the soil P content, the higher was the efficiency of nutrient recycling in M1 Chinese fir clones and the stronger was the resistance phosphate starvation; PUE of M4 Chinese fir clones showed a slowly increasing trend, PUE reached 2.41 g·kg-1 in treatment of P0, respectively, were 12.88 %, 4.64 % and 6.54 % larger than those in treatments of P3, P1 and P0. Through comparison of PUE of M1 and M4 Chinese fir clones in different treatments of P, PUE of M4 Chinese fir clones was all larger than that of M1 Chinese fir clones, and this might be related to their different ability to activate Fe-P.17,Different heterogeneity of phosphorus supplied treatments had obvious impact on differences of physiological indicators of M1 and M4 Chinese fir clones. The differences of physiological indicators in M1 Chinese fir clones impacted by heterogeneity of different treatments of P showed as follows: In treatment of P3, total amount of chlorophyll showed a change law of increase→slowly decrease→increase; In treatments of P3 and P0, it showed the trend of slowly increase→slowly decrease. MDA content in leaves showed a change law as follows: In treatments of P3 and P0, it showed a change trend of increase→decrease; MDA content increased slowly in treatment of P2, while MDA content showed a change trend of increase→decrease→slowly increase in treatment of P1. Soluble protein content in leaves showed a change trend that: With the prolongation of stress time, the content in all treatments rapidly increased first, and then gradually decreased. APA activity in leaves showed a change law that: in different treatments of P, it all increased rapidly after slow changes, and then weakened.The differences of physiological indicators in M4 Chinese fir clones impacted by heterogeneity of different treatments of P showed as follows: Chlorophyll content all showed a change law in treatments of P as follows: increase→decrease→slowly increase; Among them, change range in treatment of P0 was small. MDA content in leaves showed a change law as follows: MDA content in different treatments all showed a slow increase→decrease in trend, in which decreasing range in treatment of P3 was largest and smallest in treatment of P0; Differences of change law of soluble protein content in leaves: With the prolongation of stress time, soluble protein content in different treatments all showed a change trend: rapid increased first, and then gradually decreased. Differences of change law of APA activity in leaves: it all increased rapidly after slow changes, and then weakened.18,Heterogeneity of different P treatments had obvious impact on difference of MDA content in leaves of M1 and M4 Chinese fir clones. With the prolongation of test time, M1 Chinese fir clones showed a trend of increase→decrease in treatments of P2 and Fe0; MDA content increased slowly in treatment of Fe2, while MDA content showed a change trend of increase→decrease→slowly increase in treatment of Fe1. Before the 40 days stress, MDA content of M4 Chinese fir clones in different treatments showed a slow increase→decrease in trend, in which decreasing range in treatment of P2 was largest and smallest in treatment of Fe0; Later MDA content increased slowly in treatment of P2 and showed a decrease trend in other treatments, then MDA content in different treatments tended to the same level to the 60 days stress.19,Different treatments of heterogeneous P had no obvious impact on difference of soluble protein content in leaves of M1 and M4 Chinese fir clones. With the prolongation of stress time, soluble protein content in different treatments all showed a change trend: rapid increased first, and then gradually decreased. Stress to 60 days, soluble protein content in leaves of M1 Chinese fir clones was largest with the value of 2.403 mg·g-1 in treatment of Fe2, which were 0.471 mg·g-1, 0.690 mg·g-1 and 0.365 mg·g-1, respectively, larger than those in treatments of P2, Fe1 and Fe0; It showed that soluble protein content in leaves of M1 and M4 Chinese fir clones was differently impacted by the low-phosphorus stress.20,Different treatments of heterogeneous P had a little impact on differences of APA activity in leaves of M1 and M4 Chinese fir clones, all showed a change law that :increased rapidly after slow changes, and then weakened. Before the stress of 20 days, differences between different treatments was not obvious; Stress to 40 days, APA activity in M1 Chinese fir clones in treatment of P2 was strongest, up to 67.155 g-1·min-1, which were 111.94 %, 55.19 % and 103.40 % larger than those in treatments of Fe2, Fe1 and Fe0.While APA activity in M4 Chinese fir clones was strongest in treatment of Fe0, which were 44.70 %, 4.55 % and 34.67 % larger than those in treatments of P2, Fe2 and Fe1; To the end of the stress, APA activity in different treatments tended to the same level.21,In low-phosphorus stress conditions, with the prolongation of stress time, pH of hydroponics nutrient solution of Chinese fir showed a change law of rise first then fall. Compared to non-phosphorus and non-calcium treatment ofâ…¥, treatment of calcium supplied helped to regulate the physiological activity of the roots of Chinese fir and promote to secrete acid materials of root. At the fourth week of low-phosphorus stress, pH value of 0.074 mol·L-1 in the treatment ofâ…¢(3.0 mmol·L-1) ranked the highest level, pH value came next in treatments ofâ… (7.0 mmol·L-1) andâ…¡(5.0 mmol·L-1), respectively, 0.007 mol·L-1 and 0.008 mol·L-1 less than the former, so the differences among the three were very little; pH value in treatment ofâ…¥was only 35.14 % of that in treatment ofâ…¢. From the above it was clear that treatment of high-calcium supplied helped roots of Chinese fir to secrete acid materials in adversity of low-phosphorus conditions.22,Allocation and utilization of the amount of P accumulation in Chinese fir were affected by different Ca gradient in low-phosphorus stress as follows: With the decreases of Ca gradient, the percentage accounted by the amount of P accumulation in roots reduced in order at first and then increased; the change law of leaves and stems was not obvious, but they always declined in the opposite direction. In different Ca gradient, the PUE in treatment ofâ… was highest, amounting to 0.987 kg·g-1, differences in the remaining six treatments were not significant, of which PUE in CK was lowest with the value of 0.717 kg·g-1, it showed that the high calcium treatment had a certain impact on PUE in Chinese fir in low-phosphorus stress, but the change law was not obvious, this might be related to sustainable P-deficiency in hydroponics environment and short period of test, but this subjected to a further study.23,The study of response of low-phosphorus stress of Chinese fir impacted by different Ca gradients showed that: In low-phosphorus stress conditions, with the prolongation of stress time, pH of hydroponics nutrient solution of Chinese fir showed a change law of rise first then fall. Compared to non-phosphorus and non-calcium treatment ofâ…¥, treatment of calcium supplied helped to regulate the physiological activity of the roots of Chinese fir and promote to secrete acid materials.With the decreases of Ca gradient, the percentage accounted by the amount of P accumulation in roots reduced in order at first and then increased; the change law of leaves and stems was not obvious, but they always declined in the opposite direction. In different Ca gradient, the PUE in treatment ofâ… was highest, amounting to 0.987 kg·g-1, differences in the remaining six treatments were not significant, of which PUE in CK was lowest with the value of 0.717 kg·g-1, it showed that the high calcium treatment had a certain impact on PUE in Chinese fir in low-phosphorus stress, but the change law was not obvious, this might be related to sustainable P-deficiency in hydroponics environment and short period of test. With the reduce of Ca concentration in hydroponics, MDA content in leaves of Chinese fir in low-phosphorus stress showed the trend as follows: decrease→increase→decrease, and the change law of total chlorophyll was similar to MDA. Change law of soluble protein content in leaves of Chinese fir was similar to that of the APA activity, the overall trend was: decrease→increase→decrease. The impact of interaction of Ca and P on response of low-phosphorus stress of Chinese fir needed a further study.
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