模拟增温对杉木幼树生长和光合特性的影响

Effect of soil warming on growth and photosynthetic characteristics of Cunninghamia lanceolata saplings

为阐明杉木生长特征及光合能力对未来全球变暖的响应方式,通过在福建省三明市森林生态系统与全球变化研究站陈大观测点内开展的土壤增温(电缆加热,+4℃)实验,研究了增温条件下杉木幼树生长(树高、地径)特征及光合作用参数的变化,并对土壤有效氮(N)、叶片N含量、叶绿素含量(Chl)及非结构性碳水化合物(NSC)指标进行了测定。结果表明:1)在增温条件下,杉木幼树净光合速率(P_n)和水分利用效率(WUE)显著增加,分别增加了71.4%、51.3%,增温后杉木叶片能维持较高的气孔导度(G_s)、蒸腾速率(T_r)和胞间二氧化碳浓度(C_i)。2)增温促进土壤有机氮矿化作用,使土壤中可供植物吸收利用的有效N含量显著增加,从而引起杉木叶片N含量显著提高。而N作为叶绿素的重要组成物质,增温后,叶片N含量显著提高,最终导致杉木幼树叶片Chl a、Chl b及Chl总量显著增加,增加比例分别为76.3%、55.8%、68.7%,Chl a/b值亦呈增加趋势。3)增温对杉木幼树生长及叶片NSC含量并无显著影响。综上所述,增温通过改变杉木叶片气孔导度敏感性以及促进杉木叶片Chl含量合成,增加叶片对CO_2的吸收以及光能捕获能力,进而提高光合效率。同时,增温引起的根系高温可能大幅度提高杉木呼吸强度,加剧对杉木叶片碳水化合物的消耗过程,使其NSC含量无显著变化,从而导致杉木幼树生长无显著差异。

Global warming has a strong effect on forests,an important part of the terrestrial ecosystem,because temperature change easily influences photosynthesis.At present,most studies about global warming′s effects on photosynthesis are concentrated in high latitudes and alpine regions,with few reports from subtropical forests.Cunninghamia lanceolata is the main species used in afforestation in subtropical China.To clarify how C.lanceolata growth and photosynthesis respond to future global warming,we conducted a soil warming(cable heating,+4℃)experiment at Chenda observation point in the Sanming Research Station of Forest Ecosystem and Global Change,Fujian Province.We estimated growth variables(tree height and ground diameter),variation in photosynthesis,soil inorganic nitrogen(N)content,leaf N content,chlorophyll content(Chl),and non-structural carbohydrates(NSC).The results showed that under soil warming,net photosynthetic rate(Pn)and water use efficiency(WUE)of C.lanceolata seedlings increased by 71.4%and 51.3%,respectively.Additionally,stomatal conductance(Gs),transpiration rate(Tr),and intercellular carbon dioxide concentration(Ci)were maintained at high levels.Increasing soil temperature also promoted the mineralization of soil organic N,elevating available N for plant absorption and use.These changes caused significant increase in N content of C.lanceolata leaves.Because N is a major chlorophyll component,we also observed a notable increase in total Chl a,Chl b,and Chl by 76.3%,55.8%,and 68.7%,respectively.The ratio of Chl a to b also increased.Soil warming did not significantly alter tree height,ground diameter,and leaf NSC content of C.lanceolata seedlings.In summary,soil warming improves C.lanceolata photosynthetic efficiency through altering stomatal conductance sensitivity and promoting Chl synthesis in leaves,thus increasing CO2 absorption and light capturing ability.Simultaneously,warming-induced elevation in rhizosphere temperature may significantly increase respiration rate,accelerating carbohydrate consumption.Therefore,even after three months of soil warming,leaf NSC content and sapling growth did not significantly change.This experiment demonstrates that C.lanceolata growth and photosynthetic capacity adapts to global warming,providing a reference for predicting potential carbon sequestration of subtropical plantations in China.