喀斯特地区土壤厚度降低和水分减少对两种草本植物混种后光合的影响

土壤"厚薄不均"和"岩溶干旱"是影响喀斯特地区植物生存、生长和繁殖的关键生态因子,深根植物和浅根植物由于根系生态位的互补可能会缓解资源减少对光合作用的抑制作用。以盆栽深根植物苇状羊茅(Festuca arundinacea)和浅根植物多年生黑麦草(Lolium perenne)为对象,研究土壤厚度降低、水分减少及土壤厚度和水分双重资源减少对两种草本植物混种下其光合作用的影响。结果表明,1)在高资源水平下,混种后苇状羊茅的净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)和水分利用效率(WUE)与单种间无显著差异(P0.05);而黑麦草的Pn、Gs和Tr低于单种,WUE显著高于单种(P0.05)。2)随着资源的减少,不管是单种还是混种,苇状羊茅和黑麦草的P_n、G_s和Tr大体上均呈降低的趋势,黑麦草的WUE呈上升趋势,且混种后降低或升高的幅度明显低于单种;而苇状羊茅的WUE由单种时升高变为混种时降低。3)在低资源水平下,混种后苇状羊茅的P_n、G_s和T_r高于单种,WUE低于单种;黑麦草的P_n、G_s和T_r与单种无显著差异,WUE低于单种。研究表明,在干旱和土壤贫瘠日趋严重的喀斯特地区,通过深浅不同根系的植物混种,可能在一定程度上缓解水分和土壤资源缺乏对植物光合作用的抑制作用。

Effect of decline in soil depth and water resource on the photosynthesis of two grasses under mixed plantation in Karst regions

Uneven soil depth and karst drought are key ecological factors affecting plant survival, growth, and reproduction in karst regions.The change in global precipitation patterns will exacerbate the frequency and intensity of karst drought.The amount of water and nutrients absorbed and transported to the aboveground parts by roots systems can affect plant photosynthesis.Shallow-rooted plants mainly use water and nutrients from the top layers of the soil, whereas deep-rooted plants can use water and nutrients from the deeper soil layers.Therefore, when deep-rooted plants and shallow-rooted plants coexist, they might alleviate the inhibitory effect of resource limitation on plant photosynthesis because of their complementary root niche.We grew Festuca arundinacea (deep-rooted) and Lolium perenne (shallow-rooted) under normal versus shallow soil depth and well watered versus drought treatments in a block design, and studied the effect of the decline in soil depth, water availability, and both these resources (soil depth plus water availability) on the photosynthesis of two grasses under mixed plantation by controlled experiment.The results showed that: 1) at high resource levels, no significant difference occurred in net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and water use efficiency (WUE) of F.arundinacea between mixed plantation and in monoculture (P>0.05);Pn, Gs, and Tr of L.perenne was lower in mixed plantations than in monoculture, whereas WUE was significantly higher in mixed plantations than in monoculture (P>0.05).2) Overall, Pn, Gs, and Tr of F.arundinacea and L.perenne decreased and WUE of L.perenne increased with the decline of resources (soil depth, water, and soil depth plus water) either in mixture or in monoculture.Moreover, the range of decrease or increase was lower in mixed plantations than in monoculture;WUE of F.arundinacea increased in monoculture but decreased in mixed plantations.3) At low resource levels, Pn, Gs, and Tr of F.arundinacea was higher in mixed plantations than in monoculture, whereas WUE was lower in mixed plantations than in monoculture.No significant difference was found in Pn, Gs, and Tr of L.perenne between mixed plantations and monoculture, whereas WUE was higher in mixed plantations than in monoculture.Our results showed that owing to the complementary niche and hydraulic lift of deep-rooted plants, the inhibitory effect of resource limitation on photosynthesis of the deep-rooted and shallow-rooted plants are alleviated when they are planted together, but at the expense of WUE.Therefore, in karst regions, mixed planting with plant of different root depth systems may be an effective method of resolving the increasing drought and poor soil conditions.