闽江口互花米草淤积作用对其自身和短叶茳芏残体分解及硫养分释放的影响

2016—2017年,以闽江口鳝鱼滩西北部互花米草(SA)入侵初期与短叶茳芏(CM)形成的典型交错带植物残体为研究对象,基于野外原位分解试验,通过设定无淤积强度(S_0,0 cm/a)、当前淤积强度(S_5,5 cm/a)和未来淤积增强(S_(10),10 cm/a)3种处理,模拟互花米草入侵初期导致的淤积作用对其自身以及短叶茳芏残体分解及硫养分释放的影响。结果表明,随着互花米草入侵导致的淤积强度的增加,互花米草和短叶茳芏残体的分解速率均明显降低;与S_0相比,二者在S_5与S_(10)处理下的分解速率分别降低49.09%(SA)、35.14%(CM)和56.36%(SA)、44.59%(CM)。随着淤积强度的增加,互花米草和短叶茳芏残体分解过程中的TS含量整体均呈增加趋势,且其对短叶茳芏TS含量变化的影响较为明显;互花米草和短叶茳芏残体在分解过程中均表现为不同程度的硫释放,但随淤积强度的增加,二者硫释放量均呈降低趋势,且在相同淤积强度下,前者的硫释放量要高于后者。不同淤积强度下残体分解速率及硫养分释放强度的差异不仅与分解环境中的EC密切相关,且与残体残留率、初始基质质量(C/N和C/S)以及淤积导致养分条件改变而对分解过程中残体基质质量的影响有关。研究发现,随着淤积强度的增加,两种残体的分解速率及硫释放强度均降低;但在相同淤积强度下,短叶茳芏残体的分解速率和硫释放量均大于互花米草。

Effects of siltation by Spartina alterniflora invasion on decomposition of and sulfur release by S. alterniflora and Cyperus malaccensis in tidal marshes of the Min River Estuary

During 2016-2017, two typical plant litters (Spartina alterniflora (SA) and Cyperus malaccensis (CM)) in ecotone formed by SA invasion in Northwest Shanyutan of the Min River Estuary were studied. Furthermore, the effects of siltation by SA invasion on decomposition of and sulfur (S) release from different litters were determined by in situ decomposition experiment, which included three one-off siltation treatments[no siltation treatment (0 cm/a, S₀), current siltation treatment (5 cm/a, S₅), and strong siltation treatment (10 cm/a, S₁₀)]. The results showed that the decomposition rate of SA and CM litters significantly decreased with increase in siltation depth. Compared with that in the S₀ treatment, the decomposition rate in the S₅ and S₁₀ treatments decreased by 49.09% (SA) and 35.14% (CM), and 56.36% (SA) and 44.59% (CM), respectively. The content of TS in SA and CM litters generally increased with increase in siltation depth, but the values in CM litter increased by a large margin. The net release of S in SA and CM litters in different siltation treatments was observed throughout the decomposition process and the release amount generally decreased with increase in siltation depth. However, in the same siltation treatment, S release from SA was significantly higher than that from CM. The differences in decomposition rate and S release amount of the two litters in different siltation treatments depended not only on the sediment EC in decomposing environments, but also on the dry mass remaining, initial substrate quality (C/N and C/S), and variations in substrate quality caused by the alteration of nutrient conditions. We found that both the decomposition rate and S release from the two litters decreased with increase in siltation depth, but with the same siltation treatment, the decomposition rate and S release from CM were higher than those of SA.