Response Of Belowground Net Primary Productivity And Root Dynamics To Different Restoration Measures

Grassland ecosystem,which plays a significant role in global carbon cycle as well as climate regulation,is the most widely carbon distribution ecosystem.Songnen grassland,is a symbolic meadow steppe,which is inside China's Northeast Plain.Salinization is caused by both natural and human factors,and the degree of salinity increases over the years.Regarding the ecological recovery for the salinization of Songnen grassland,lots of work and studies were carried out which primarily focused on aboveground.However,no studies were conducted from the whole plant perspective,namely belowground net primary productivity?BNPP?and root dynamics.Our studies engaged six experimental treatments which were haphazardly organized in this manner:free grazing?FG?,no ploughing?NP?,only ploughing?OP?,ploughing with fertilizer?PF?,ploughing+mulching?PM?,ploughing with mulching and fertilizer?PFM?.Each of the abovementioned treatment was carried out four times.BNPP and root turnover were determined using root ingrowth donuts and improved root window's method respectively.From the whole plant aspect,we analyzed the variation of aboveground and belowground in the recovery course,in particular for the reaction of root dynamics to varied recovery measures.The outcomes will make the reaction of roots in belowground ecological recovery theory more complete and enhance our familiarity with belowground grassland ecology.Based on the three-year results,the major outcomes are shown below:1.During the three-year recovery span,the growth of Chloris virgata and Suaeda glauca every year are prevailing and a few perennial plant of Puccinellia tenuiflora.The highest relative density of Chloris virgata is 99.4%,and the density of Suaeda glauca is 89.6%.Chloris virgata is the single dominant species in those restoration measures The outcome indicates that PFM helps in growth and recovery of aboveground vegetation.2.Although there was no differences between different restoration measures,soil pH and EC reduced from 2011 to 2014,pH was from 10.5 to 10.0,and EC was from 2112 mS cm-1 to247 mS cm-1,indicating that physicochemical environment of the experimental soil is improved.3.Given varied recovery treatment,the maximum BNPP values for 2012-2014 were 43.4g m-2,29.6 g m-2 and 40.4 g m-2,respectively.The recovery is not stable due to majority coverage of annual vegetation and minimum perennial vegetation.Year of vegetation and treatments cast compelling effects on BNPP?P<0.01?.BNPP in 2014 was 1.66 times of 2012and 2013,but ANPP of 2014 was significantly lower than that of 2012 and 2013?P<0.05?.the increases of BNPP and decrease of ANPP is mainly due to precipitation amount.Under drought conditions,more photosynthesis product was distributed to the underground,and plants need more fine roots for absorbing more water and nutrients in low rainfall condition.Furthermore BNPP was significantly different between different restoration treatments?P<0.01?.PFM restoration treatment had the highest BNPP and ANPP.So ploughing,mulching and fertilizer can increase the productivity.4.The root dynamics were significantly changed with the seasons.In July,root productivity,root mortality and root standing crop all reached a peak both in the 0-10 cm and10-20 cm soil layers.In the growing season,plants produce more roots and increase root standing crop to absorb water and nutrients better.At the same time,a large number of roots died.The investment in the root system gradually decreased can provide more organic matter into the aboveground for photosynthesis.5.Varied recovery methods had no prominent effect on root turnover.Root turnover is0.76 yr^-1 in 2014,significantly increased than 0.62 yr^-1 in 2013.Those results indicate that different restoration treatments did not have an effect on root turnover in a short time,but it was significantly affected by the amount of rainfall.PFM restoration treatment significantly increased root productivity,mortality and standing crop,showing PFM can improve plant growth environment,and create growth condition for roots,finally help the restoration of saline-alkali grassland.In summary,the combination of ploughing,mulching and fertilizer can help lessen the salinity and pH of surface soil?0-2 cm?,achieve higher ANPP,BNPP,vegetation coverage and species density,but had no effect on root turnover.Hence,these are applicable recovery methods for annual vegetation.In order to obtain stable perennial grass,a more long-term recovery,chemical and physics recovery methods are required.