高寒草甸不同演替阶段优势种叶片光合性状研究

Photosynthetic Traits of Dominant Species in Alpine Meadow along A Successional Stage

围封年限不同导致形成以不同优势种植物建立的群落样带。按照植被的演替序列(围封1、3、5、15、30 a),在甘南高寒草甸选择不同演替阶段的优势植物:刺儿菜(Cirsium setosum)、披碱草(Elymus nutans)、紫花苜蓿(Medicago sativa)、沙蒿(Artemisia desertorum)和金露梅(Potentilla fruticosa),对其叶片光合性状进行了测定,探究植物叶片光合性状与环境因子之间的关系,旨在确定演替过程中控制植物光合性状变化的主要环境因子,为进一步促进高寒草甸草地恢复年限的设定及草地资源的可持续利用提供科学依据。结果表明,随着植被演替的进行,群落形成了以草本→半灌木→灌木为主的演替序列。表层(0～20 cm)土壤含水量(SWC)随演替进行呈增大趋势,变化范围为0.323～0.390 g·g^(-1);土壤温度(t_s)和光照强度(I_l)在前期最大(23.974℃;90.382 lx),后期最小(20.310℃;65.220 lx)。各演替阶段优势种光合特征值在时间尺度上除相对叶绿素外均存在明显差异,草本群落优势种(刺儿菜、披碱草、紫花苜蓿)净光合速率(Pn)高于灌丛群落优势种(金露梅),瞬时水分利用效率(WUEi)与Pn变化规律相似。蒸腾速率(T_r)与稳定碳同位素(δ13C)呈缓慢降低趋势,分别降低2.128 mmol·m^(-2)·s^(-1)、4.359‰。各演替群落优势种叶片气孔导度(Gs)随演替的进行逐步升高,最大值为0.155mol·m^(-2)·s^(-1);叶片含水量呈先升高后降低趋势,演替15年最大(5.207g·g^(-1));而相对叶绿素(SPAD)呈先降低后稳定趋势。在植被演替进程中,LWC、G_s与SWC呈正相关,δ^(13)C、T_r、P_n、WUE_i、SPAD与SWC呈负相关,t_s、I_l与SPAD、T_r、P_n、WUE_i、δ^(13)C呈正相关,与LWC、G_s呈负相关。环境因子对植物叶光合性状的影响大小为I_l>SWC>t_s,这表明光照度是该区演替发生及影响光合性状的主要因子。综合分析表明,群落演替是物种扩散和环境综合作用的过程,该围封地由物质获得能力强的群落向物质保持能力强的群落过渡,围封5～15 a群落环境最优。

Different enclosure years leads to the formation of community transects with different dominant species.According to the succession sequence of vegetation(1,3,5,15,30 a),the dominant plants at different successional stages were selected respectively in alpine meadow of Gannan:Cirsium setosum,Elymus nutans,Medicago sativa,Artemisia desertorum,Potentilla fruticosa in different successional stages.The photosynthetic characteristics of dominant plant leaves were measured,according to the succession sequence in the alpine meadow of Gannan.The relationship between plant photosynthetic characteristics and environmental factors was explored to determine the main environmental factors during succession.The results showed that successional sequences(herbaceous→semi-shrubs→shrubs)were formed with the community change,soil water content(SWC)at 0-20 cm increased,the range of variation was 0.323-0.390 g·g^-1,and soil temperature(ts)and light intensity(Il)were the highest at the early stage(23.974℃;90.382 lx),and the lowest at the later stage(20.310℃;65.220 lx).The photosynthetic traits of the dominant species were significantly different on the time scale.The net photosynthetic rate(Pn)of the dominant species(Cirsium setosum,Elmus dahuricus,Medicago sativa)was higher than scrubs community(Potentilla fruticosa),and instantaneous water use efficiency(WUEi)were similar to the Pn.The transpiration rate(Tr)and the stable carbon isotope(δ^13C)showed a decreasing trend,the reduction were 2.128 mmol·m^-2·s^-1 and 4.359‰respectively.The leaf stomatal conductance(Gs)was lower in the early stage,and gradually increased in the late stage,with the maximum of 0.155 mol·m^-2·s^-1.The water content of leaves increased first and then decreased,with the maximum at 15 years(5.207 g·g^-1).The relative chlorophyll(SPAD)decreased first,followed by a steady trend.LWC,Gs and SWC were positively correlated in the course of succession,andδ^13C,Tr,Pn,WUEi,SPAD were negatively correlated with SWC.ts,Il was positively correlated with SPAD,Tr,Pn,WUEi andδ^13C,but negatively correlated with LWC and Gs.The influence of environmental factors on leaf photosynthetic characteristics were as follows:Il >SWC >ts,these characteristics indicated that light intensity was the main factor affecting photosynthetic traits in succession stage.The comprehensive analysis showed that the community succession was a process from species dispersal and environment effect.The meadow enclosure was transformed from a community with the strong ability of material acquisition to the strong ability of material conservation.The optimal enclosure environment would be in 5-15 years.