| Masson pine(Pinus massoniana)is a native fast-growing conifers with excellent timber quality high pine resin yield.Its area of natural forest and plantations(about 10.01 million hm2)has expanded rapidly to reach an estimated area of 10.01 million hm2.Which supporting China's development in wood processing,pulping and papermaking,forest chemical industry and so on.However,the phosphorus in forest soil is mostly severe scarcity,meanwhile,atmospheric nitrogen dramatically raised recently has seriously affected the sustaintable forest management.Taking different representative clones(families)of P.massoniana as test materials,a pot experiments consisting of homogeneous low phosphorus stress(low phosphorus level in all soil layers)and heterogeneous low phosphorus stress(high phosphorus level in the topsoil and low phosphorus level in the bottom soil)conditions were designed and conducted to investigate variations of growth,root morphology,fine-root parameters and phosphorus(nitrogen)efficiency in response to nitrogen addition and localized nitrogen supply,respectively.Therefore,the results may reflect the difference in response to nitrogen addition and localized nitrogen supply among different genotypes.This study aims to privide theoretical foundation for selecting and breeding of favorite genotypes with higher nutrient efficiency in the context of atmospheric nitrogen deposition,and offer scientific guidance for expanding rapidly of planted-forest's intensive management.The main results are as follows:The adaptive mechanism of P.Massoniana clones in response to nitrogen addition was different under different types of low soil phosphorus.Under the homogeneous low phosphorus condition,the adaptive responses of root length,root surface area and APase activity were present in clones with strong growth vigor by nitrogen addition such as "33-4" and "19-5",while it was not observed in clones with weak growth vigor.Meanwhile,the correlation between dry matter accumulation and APase activity was enhanced by the nitrogen addition.Under the heterogeneous low phosphorus condition,root length and root surface area were significantly improved by the nitrogen addition,while the special root length was decreased,thus got the greater capacity for nutrition absorption and having lower consumption.The phosphorus absorption efficiency of P.massoniana clones was significantly affected by the nitrogen addition and showed a significant positive correlation with nitrogen absorption efficiency under different N-P conditions(P<0.01).It indicated that the nitrogen addition could increase the phosphorus mobilization and uptake of P.massoniana clones under the phosphorus deficiency.In contrast,there was no significant effect on phosphorus use efficiency.The fine-root growth was more senstive to the change of nutrient in soil which conducted by nitrogen addition.Our experiment disclosed that,nitrogen addition affected seedling growth,along with significant interactive effects among nitrogen supply level,phosphorus condition and genotypes.Under heterogeneous phosphorus deficiency,the seedling height and dry weight of clone 19–5 were 1.10 times and 1.60 times higher than that of clone 21–3,respectively.Nitrogen addition significantly simulated fine root proliferation in fine-root diameter class of ?1.5 mm,while roots with diameters ranged from 1.5 to 2.0mm and over 2.0 mm did not show apparent change.Fine root(?1.5 mm)length accounted for 90.46%–92.80% of the total and held constant.Under the heterogeneous low phosphorus condition,clone 19–5 was found to respond to the nitrogen addition with increased root length and surface area in fine-root diameter class of ?1.5 mm.What' more,in compared with control,its nitrogen and phosphorus absorption efficiency were significantly enhanced 93.30% and 148.45%,respectively.However,the nitrogen and phosphorus absorption efficiency of clone 21–3 revealed less effect by the nitrogen addition.The nitrogen and phosphorus use efficiency had no notable variation.Finally,we found that fine-root(?1.5 mm)proliferation and high nitrogen(phosphorus)absorption efficiency of P.massoniana maybe the adaptive mechanisms to response to nitrogen addition under phosphorus deficiency.Nutrient distribution has been affected by the nitrogen addition,coupled with nitrogen level in soil.The effects of localized nitrogen addition and homogenous nitrogen addition on plant growth and root parameters were studied by carrying out a pot experiment.The results showed that localized nitrogen supply affected seedling growth,along with significant interactive effects among nitrogen supply pattern and phosphorus condition.In compared with homogeneous nitrogen supply(HHH),the seedling height,seedling basal diameter and seedling dry weight increased significantly by localized nitrogen supply(bottom layer nitrogen addition(LLH)and/or semi-bottom layer nitrogen addition(LLH/L)under two phosphorus deficiency,while them subjected to top and middle layers nitrogen addition(HHL)pattern under heterogeneous phosphorus deficiency were inhibited.Within the two phosphorus conditions,LLH and LLH/L stimulated root proliferation significantly and the promotion effects became stronger under heterogeneous phosphorus deficiency(in compared with HHH pattern,their root length and root surface subjected to LLH/L were significantly enhanced 29.2% and 32.3%,respectively).However,the root length and root surface area were suppressed by HHL treatment.There were significant differences among families with different patterns of nitrogen supply.Seedlings in the families of 49,52,and 57 were found to respond to the localized nitrogen supply with stimulated root proliferation,thus enhancing greater seedling dry weight.On the other hand,the seedling growth of aboveground in the family of 25 were stimulated by nitrogen and(or)phosphorus concentration,while seedlings in the family of 1 exhibited dully responsive to nutrients patches.This study indicated that localized nitrogen supply did enhance the growth of P.massoniana,and this enhancement mainly happened in the pattern of nitrogen applied to deep soil. |
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