土壤水分和养分对沙质草地优势植物叶片氮回收效率的影响

Effects of nutrient and water content on leaf nitrogen recovery efficiency of dominant plants in sandy grasslands

气候变化和人类活动影响草地资源利用效率和内部养分循环。为了明晰中国半干旱草原区植物对环境变化的养分调控策略,以沙质草地4种优势植物[狗尾草(Setaria viridis)、黄蒿(Artemisia scoparia)、白草(Pennisetum centrasiaticum)和糙隐子草(Cleistogenes squarrosa)]为研究对象,依托增减水和氮添加交互模拟试验平台,分析了降水变化、氮添加及其耦合效应下土壤水分、土壤全氮、优势植物地上生物量、绿叶和枯叶氮含量以及氮回收效率(NRE)。结果表明:降水变化和氮添加及其耦合效应会引起物种结构和组成的变化,最终影响优势植物的生产力;干旱处理条件下,氮添加显著提高了狗尾草的绿叶氮含量从而降低NRE(P<0.05);生长季前期(5—6月)增加降水100%(+60 d)处理下,氮添加显著提高了黄蒿的绿叶氮含量(P<0.05);对于白草而言,生长季前期(5—6月)减少降水100%(-60 d)、CK和+60 d处理下,氮添加显著提高了绿叶氮含量(P<0.05),CK和+60 d处理下,氮添加显著提高了枯叶氮含量(P<0.05),+60 d处理下,氮添加显著降低了NRE(P<0.05);对于糙隐子草而言,CK处理下,氮添加显著提高了绿叶氮含量(P<0.05),+60 d处理下,氮添加显著提高了枯叶氮含量(P<0.05)。结构方程模型(SEM)表明,降水量对绿叶氮含量有负向影响,氮添加对绿叶氮含量和枯叶氮含量均有正向影响,绿叶氮含量对NRE有正向影响,而枯叶氮含量对NRE有负向影响。在科尔沁沙地,相比较于土壤氮,土壤水分可能是调控植物叶片NRE更为重要的影响因子。

Climate change and human activities will affect grassland resource use efficiency and internal nutrient cycling.In order to clarify the nutrient regulation strategies of plants in the semi-arid grassland region of China,this study took four dominant plants(Setaria viridis,Artemisia scoparia,Pennisetum centrasiaticum,Cleisto-genes squarrosa)in sandy grassland as the research objects,and based on the interactive simulation test platform of increase or decrease precipitation and nitrogen addition,the soil moisture content,soil total nitrogen content,dominant plants'aboveground biomass,leaf nitrogen concentration in mature leaves,leaf nitrogen concentration in senescent dead leaves,and nitrogen resorption efficiency(NRE)were analyzed.The results showed that nitro-gen addition promoted biological activity and increased soil water content(P<0.05)under natural precipitation(CK)or drought treatment conditions.Precipitation changes and nitrogen addition and their coupling effects will cause changes in species structure and composition,which ultimately affect the productivity of dominant plants.Under drought treatment,nitrogen addition significantly increased the nitrogen content in mature leaves of Setar-ia viridis and reduced the NRE(P<0.05).Under the treatment of increasing precipitation by 100%(+60 d)in the early growing season(May to June),nitrogen addition significantly increased the mature leaf nitrogen con-tent of Artemisia scoparia(P<0.05).For the Pennisetum centrasiaticum,the nitrogen addition significantly in-creased the nitrogen content in mature leaves under decreasing precipitation by 100%(-60 d)in the early grow-ing season(May to June)(P<0.05),and the nitrogen addition significantly increased the nitrogen content of se-nescent dead leaves(P<0.05)under CK and+60 d treatment,and the nitrogen addition significantly reduced the NRE under+60 d treatment(P<0.05).For Cleistogenes squarrosa,nitrogen addition significantly increased the nitrogen content in mature leaves under CK treatment(P<0.05),and nitrogen addition significantly increased the nitrogen content of senescent dead leaves under+60 d treatment(P<0.05).The structural equation model(SEM)showed that precipitation had a positive effect on soil moisture and a negative effect on nitrogen content in mature leaves,nitrogen addition had a positive effect on the nitrogen content in mature leaves,soil moisture and the nitrogen concentration in senescent dead leaves,and the nitrogen content in mature leaves had a positive effect on NRE,and the nitrogen content of senescent dead leaves had a negative effect on NRE.In the Korqin Sandy Land,soil moisture may be a more important influencing factor in regulating the NRE of plant leaves than soil nitrogen.