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Living, dead, and absent trees—How do moth outbreaks shape small-scale patterns of soil organic matter stocks and dynamics at the Subarctic mountain birch treeline?
Global Change Biology ( IF 11.6 ) Pub Date : 2021-10-21 , DOI: 10.1111/gcb.15951
Nele Meyer 1, 2 , Yi Xu 1 , Katri Karjalainen 3 , Sylwia Adamczyk 1, 4 , Christina Biasi 3 , Lona van Delden 3, 5 , Angela Martin 1 , Kevin Mganga 1, 6 , Kristiina Myller 3 , Outi-Maaria Sietiö 1 , Otso Suominen 7 , Kristiina Karhu 1, 8
Affiliation  

Mountain birch forests (Betula pubescens Ehrh. ssp. czerepanovii) at the subarctic treeline not only benefit from global warming, but are also increasingly affected by caterpillar outbreaks from foliage-feeding geometrid moths. Both of these factors have unknown consequences on soil organic carbon (SOC) stocks and biogeochemical cycles. We measured SOC stocks down to the bedrock under living trees and under two stages of dead trees (12 and 55 years since moth outbreak) and treeless tundra in northern Finland. We also measured in-situ soil respiration, potential SOC decomposability, biological (enzyme activities and microbial biomass), and chemical (N, mineral N, and pH) soil properties. SOC stocks were significantly higher under living trees (4.1 ± 2.1 kg m²) than in the treeless tundra (2.4 ± 0.6 kg m²), and remained at an elevated level even 12 (3.7 ± 1.7 kg m²) and 55 years (4.9 ± 3.0 kg m²) after tree death. Effects of tree status on SOC stocks decreased with increasing distance from the tree and with increasing depth, that is, a significant effect of tree status was found in the organic layer, but not in mineral soil. Soil under living trees was characterized by higher mineral N contents, microbial biomass, microbial activity, and soil respiration compared with the treeless tundra; soils under dead trees were intermediate between these two. The results suggest accelerated organic matter turnover under living trees but a positive net effect on SOC stocks. Slowed organic matter turnover and continuous supply of deadwood may explain why SOC stocks remained elevated under dead trees, despite the heavy decrease in aboveground C stocks. We conclude that the increased occurrence of moth damage with climate change would have minor effects on SOC stocks, but ultimately decrease ecosystem C stocks (49% within 55 years in this area), if the mountain birch forests will not be able to recover from the outbreaks.

中文翻译:

活的、死的和缺席的树木——飞蛾爆发如何塑造亚北极山桦树线的土壤有机质储量和动态的小规模模式?

山桦林(Betula pubescens Ehrh. ssp. czerepanovii) 在亚北极林线,不仅受益于全球变暖,而且越来越多地受到以树叶为食的几何蛾的毛毛虫爆发的影响。这两个因素对土壤有机碳 (SOC) 储量和生物地球化学循环都有未知的影响。我们测量了芬兰北部活树下和死树(蛾爆发后 12 年和 55 年)和无树苔原的两个阶段的基岩 SOC 储量。我们还测量了原位土壤呼吸、潜在的 SOC 可分解性、生物(酶活性和微生物生物量)和化学(N、矿物 N 和 pH 值)土壤特性。活树下的 SOC 储量 (4.1 ± 2.1 kg m²) 明显高于无树苔原 (2.4 ± 0.6 kg m²),并且即使在 12 (3.7 ± 1.7 kg m²) 和 55 年 (4.9 ± 3 . 0 kg m²) 树木死亡后。树木状况对 SOC 储量的影响随着与树木距离的增加和深度的增加而降低,也就是说,树木状况对有机层的影响显着,但在矿质土壤中没有。与无树苔原相比,活树下的土壤具有更高的矿物质氮含量、微生物生物量、微生物活性和土壤呼吸作用;枯树下的土壤介于这两者之间。结果表明,活树下的有机物质周转加快,但对 SOC 储量有积极的净影响。有机物周转放缓和枯木的持续供应可能解释了为什么死树下的 SOC 储量仍然较高,尽管地上碳储量大幅减少。
更新日期:2021-12-13
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