沙质草地不同生活史植物的生物量分配对氮素和水分添加的响应

以氮素和水分(冬季增雪和夏季增雨)为控制因子, 开展相关田间控制实验, 分析不同功能群(以生活史为划分依据)尺度和群落尺度植物生物量分配格局对氮素和水分的响应, 得出以下结论: 1)一年生植物的繁殖生物量比重明显高于多年生植物, 而多年生植物种的叶/地上生物量比值显著高于一年生植物; 2)一年生植物对氮素和水分添加的响应剧烈, 氮添加耦合夏季增雨、氮添加耦合冬季增雪显著增加了一年生植物的繁殖生物量比重和叶生物量比重。多年生植物对氮素和水分添加的响应不敏感, 表现为多年生植物的各器官生物量分配格局对氮素添加和水分添加的响应不明显。3)氮素添加和水分处理改变了群落尺度生物量分配格局: 氮素添加耦合冬季增雪处理降低了群落植物的繁殖生物量比重和茎生物量比重, 提高了群落植物的叶生物量比重。4)冬季增雪和夏季增雨与氮素添加的交互作用对群落生物量分配格局的改变不同。夏季增雨耦合氮素添加处理下群落的茎生物量比重显著提高, 群落茎生物量分配的改变引起群落的垂直结构发生改变。冬季增雪氮素处理下群落的叶生物量比重增加, 但茎生物量比重增加不明显。冬季增雪也改变了群落的结构和功能。

Biomass allocation response of species with different life history strategies to nitrogen and water addition in sandy grassland in Inner Mongolia

Aims We examine how resources influence plant productivity and plant biomass allocation in dry sandy grasslands. Our specific objective is to determine whether 1) annual species and perennial species differ in biomass allocation in response to nitrogen and water addition and 2) if differentiation exists, how nitrogen- and water-induced changes in biomass allocation for species affect ecosystem functioning at the community scale.
Methods This experiment was established in 2010 in the central region of the Horqin sandy grassland in Inner Mongolia. Two treatments, nitrogen and water addition, were started in May, and we measured leaf traits, leaf biomass, stem biomass, stem:leaf ratio, reproductive biomass and vegetative height of the dominant species.
Important findings Biomass allocation in response to nitrogen and water differed between annual species and perennial species. With nitrogen addition the reproductive biomass of annual species decreased 75.6% and the leaf biomass of annual species increased 86.7%. Water addition did not alter biomass allocation, but the interaction of nitrogen and water did. The relative stem biomass values increased 6.2% with nitrogen addition × increased snow in winter treatment, and relative leaf biomass values increased 15.3%. In nitrogen addition × increased precipitation in summer treatments, relative stem biomass and relative leaf biomass increased 28.7% and 19.4%, respectively. Nitrogen and water addition did not alter the biomass allocation pattern of perennial species, but the interaction of nitrogen and water increased reproductive biomass 40%. Nitrogen addition altered biomass allocation at the community scale. Relative reproduction biomass decreased 39.4%, and relative leaf values increased 40.1% with nitrogen addition treatments. On average, relative stem biomass decreased 23.4% and relative leaf biomass increased 57.1% with water addition. The interaction of nitrogen and water addition also significantly altered biomass allocation. Community reproductive biomass decreased 48.3%, community stem biomass decreased 31% and community leaf biomass increased 57.5% in nitrogen × precipitation treatments. We also found that community plant height increased with added nitrogen or water, resulting in a change of community vertical structure.