Responses Of Carbon, Nitrogen And Phosphorus Allocations To Nitrogen Addition In Herbaceous Plants In Natural Secondary Forests

In order to study the nutrient utilization characteristics of herbs in Changbai Mountain secondary forest and their response to nitrogen addition,and clarify the nutrient distribution and plant species evolution strategies of understory herbs in Changbai Mountain natural secondary forest under nitrogen addition,as well as revealing the relationship between the material and energy cycle of the ecosystem,the shape and function of plants.In this study,we investigated the growth of herbaceous plants in three different levels of nitrogen treatment plots under uniform site conditions in the Lushuihe forest area in the northeast of Baishan City,Jilin Province,China.The nitrogen treatments were respectively the control,CK,0(g·m^-2·a^-1),low N,LN,2.5(g·m^-2·a^-1),high N,HN,5(g·m^-2·a^-1).Sampling experiments on herbaceous plants such as Parasenecio hastatus,Polygonatum sibiricum,Lamium barbatum Sieb,Heracleum moellendorffii Hance,Cardamine tangutorum O.E.Schulz,etc.in the sample plot.The result showed:(1)Nitrogen addition treatment generally increased the biomass of herbaceous plants and increased the productivity of herb communities in Changbai Mountain.Nitrogen addition can promote the underground development of herbaceous plants and inhibit the growth of a small number of herbaceous plant roots that have reached the nitrogen saturation point.Except for the rare Heracleum moellendorffii Hance belongs to Brassicaceae,nitrogen addition can promote the non-reproductive development and root growth of the other four common plants.It is speculated that nitrogen addition can promote the growth of most herbaceous plants in Changbai Mountain.(2)Nitrogen addition had no significant effect on the C stoichiometry of herb leaves and stems(P>0.05).Root C was easily affected by sampling or the volume ratio of stored roots to active fine roots,but showed an up-regulation trend.Leaf N content there was no significant change,the stem and root system N were up-regulation.The leaf P content did not change significantly(P>0.05),and the stem and root system P was down-regulation.(3)According to plant N:P,it can be known that the Changbai Mountain area belongs to a nitrogen-restricted environment.N:P was up-regulation,alleviating the nitrogen limitation of herbaceous plants but aggravating the phosphorus limitation.The herbaceous plant C:N was down-regulation.Adequate nitrogen sources lead to reduced plant nitrogen utilization.As far as herbaceous plants C:P was concerned,there was an up-regulation trend,and the heavier phosphorus restriction improved the phosphorus utilization of herbaceous plants.(4)The stability of C element in Changbai Mountain herbs is higher than that of N and P elements.The interaction of nitrogen addition and plant species had a significant effect on the ecological stoichiometry of plants indistinguishable organs(the content of carbon,nitrogen and phosphorus,C:N,N:P)(P<0.05).But not significant influence on the ratio of C:P and phosphorus utilization rate(P>0.05).