黄土高原生物结皮对种子出苗及幼苗存活与生长的影响

Effects of biocrusts on seedling emergence,survival and growth on the Loess Plateau,China

生物结皮可通过多种直接或间接途径影响种子出苗和幼苗生长,但相关研究多集中在极干旱沙漠及荒漠区,且多为盆栽实验。以无结皮为对照,通过野外实验分析不同盖度(80%、50%、30%)的藻结皮和藓结皮对柠条锦鸡儿(Caragana korshinskii)、黑沙蒿(Artemisia ordosica)、鬼针草(Bidens pilosa)种子出苗、幼苗存活和生长的影响,并探究其作用途径。结果表明:高盖度生物结皮更有利于种子出苗。柠条锦鸡儿和黑沙蒿种子在高盖度藓结皮上的出苗率比无结皮分别增加了1.5倍和17.5倍,柠条锦鸡儿、黑沙蒿和鬼针草种子在高盖度藻结皮上的出苗率比无结皮分别增加了1.3、14.0、0.7倍。但黑沙蒿幼苗在生物结皮上的存活率极低,可见生物结皮促进小种子出苗却对其存活不利。藓结皮对幼苗生长有促进作用,且在高盖度结皮上促进效果最好,而藻结皮则表现为高盖度促进,中、低盖度抑制。结构方程模型分析表明,生物结皮主要通过间接效应影响种子出苗和幼苗生长,且总效应均为正效应,其中幼苗存活主要受穿透阻力影响,幼苗生长主要受土壤化学性质影响。综上,生物结皮对植物种子出苗和幼苗生长的影响随物种而异,且作用效果和结皮盖度有关,但总体为促进作用,因而有利于黄土高原植被恢复和更新。

Biocrusts may affect seedling emergence and growth through direct or indirect pathways.However,most of the relevant studies have been conducted in extremely arid deserts using flower pots.To clarify whether biocrusts promote or inhibit early vegetation establishment in a relatively natural environment and to identify the pathways,we established field plots on cyanobacteria-and moss-dominated crusts,treated the biocrust cover as high,middle and low(80%,50%and 30%)and sowed the seeds of Caragana korshinskii,Artemisia ordosica and Bidens pilosa on the surface of plots.Seedling emergence percentage,survival percentage and growth rate were then calculated.The results showed that the high-cover biocrusts were more favorable for seedling emergence.In comparison with bare soil,the seedling emergence percentage of Caragana korshinskii and Artemisia ordosica increased by 1.5 and 17.5 times on high-cover moss crusts,respectively,and by 1.3 and 14.0 times on high-cover cyanobacteria crusts.The seedling emergence percentage of Bidens pilosa increased by 0.7 times on high-cover cyanobacteria crusts.However,the survival percentage of Artemisia ordosica seedlings on biocrusts was extremely low,which means that the biocrusts are beneficial for seedling emergence of small seeds,but detrimental for their survival.Overall,moss crusts increased the growth rate of seedling height and ground diameter,with the greatest enhancement on high-cover moss crusts.While cyanobacteria crusts showed promotion at high cover and inhibition at middle and low cover.Structural equation model analysis showed that the biocrusts affected seedling emergence and growth mainly through indirect effects,and the overall effects were positive.The penetration resistance was the main factor promoting seedling survival,and the soil chemical property was the main factor promoting seedling growth.In summary,the effects of biocrusts on seedling emergence and growth differed between plant species,and the effects were related to biocrust cover.But in general,the effects are favorable,making biocrusts beneficial for vegetation restoration and regeneration on the Loess Plateau.