【作者】 杨帆；

【导师】 张健； 谭波；

【作者基本信息】 四川农业大学 ， 森林培育， 2023， 博士

【摘要】 季节性雪被是调控寒冷生态系统冬季生态学过程的重要生态因子之一。气候变暖已导致北半球季节性积雪显著减少,并对寒冷生态系统季节性雪被特征(例如,雪被深度、雪被周期、覆盖面积等)产生深刻影响。地处青藏高原东缘的川西亚高山森林生态系统是响应气候变化的生态敏感区,地表雪被减少可能通过影响土壤微环境对土壤微生物生化特性和碳氮矿化过程产生强烈作用,然而其影响机制和作用机理迄今缺乏应有的关注。因此,以川西亚高山岷江冷杉针叶林为研究对象,设置野外雪被控制装置,设计自然雪被(对照)、雪被去除50%(雪被减少处理)和雪被去除100%(雪被去除处理)三种处理,采用原位土柱培养法,在2018–2020年冬季(雪被形成期、覆盖期和融化期)和生长季(前、中和后期)的关键时期研究了季节性雪被变化对岷江冷杉林中土壤有机层和矿质层的土壤微环境、微生物活性、生物量、群落组成和多样性以及土壤碳氮矿化速率的影响。主要结果如下:(1)冬季最大雪被深度为39±4cm。相较于对照,雪被减少和雪被去除处理中的雪被深度分别降低53.63%和100%。雪被处理(雪被减少和雪被去除)导致土壤更为剧烈的温度波动,雪被减少和雪被去除导致土壤有机层平均温度分别降低0.41°C和0.24°C,矿质层土壤温度分别降低0.58°C和0.47°C。雪被减少降低冬季土壤温度的效应最为显著,而雪被去除导致生长季的土壤温度偏低。雪被减少和雪被去除导致土壤冻融循环频次分别增加17.67次和15.33次,土壤含水量分别降低1.34%和13.13%,但雪被处理没有显著改变土壤p H值。(2)雪被处理仅对土壤β-葡聚糖苷酶活性影响显著,但雪被处理和采样季节的交互作用显著影响土壤β-葡聚糖苷酶、纤维素酶、脲酶和硝酸还原酶活性,且不同土壤层次间差异显著。雪被减少和雪被去除导致土壤β-葡聚糖苷酶活性降低5.23%～11.61%,脲酶活性降低8.35%～10.77%,但使土壤有机层硝酸还原酶活性增加7.58%～11.80%,土壤矿质层中其活性降低3.56%～9.88%。在冬季,雪被减少和雪被去除抑制β-葡聚糖苷酶、纤维素酶、硝酸还原酶活性,但在冬季雪被形成期促进土壤有机层脲酶活性;在生长季后期,雪被减少和雪被去除会抑制脲酶活性,并显著促进硝酸还原酶活性。雪被处理并未显著影响土壤微生物生物量碳含量,但导致土壤微生物生物量氮含量显著增加39.18%～79.18%,微生物生物量氮的增加主要发生在雪被形成期和融化期。(3)相较于对照,雪被减少和雪被去除显著增加真菌、细菌的Chao和ACE丰富度指数,真菌Chao和ACE丰度指数分别增加3.13%～6.41%和6.41%～2.54%,细菌Chao和ACE丰度指数分别增加2.12%～5.95%和2.00%～5.92%。微生物丰富度的显著改变主要发生在冬季。在门水平,雪被减少导致Basidiomycota真菌和Acidobacteria细菌丰度增加,并降低Mortierellomycota真菌、Actinobacteria细菌丰度。在属水平,雪被减少导致Boletaceae属真菌丰度增加,并降低Mortierella属真菌、Acidothermus属和Acidimicrobiia属细菌丰度。然而,雪被去除并未显著影响土壤真菌和细菌群落的群落组成。(4)雪被处理显著影响土壤碳矿化速率,但雪被减少和雪被去除对土壤氮矿化速率的影响相互对立。相较于对照,雪被减少和雪被去除导致土壤碳矿化速率降低11.39%～26.14%;然而,雪被减少使土壤氮矿化速率降低122.50%,雪被去除使其增加178.39%。此外,雪被处理显著影响土壤有机质、总氮、可溶性有机碳和可溶性有机氮浓度。雪被减少和雪被去除导致土壤有机质浓度增加30.72%～121.6%,可溶性有机氮浓度增加42.54%～132.09%。雪被减少和雪被去除导致土壤有机层可溶性有机碳浓度增加32.85%,土壤矿质层可溶性有机碳浓度降低11.42%;导致土壤有机层总氮浓度增加63.06%,土壤矿质层总氮浓度受雪被减少和雪被去除影响分别等效增加和降低9.68%。(5)偏最小二乘结构方程模型表明,雪被减少和雪被去除引起的土壤降温、酶活性降低和土壤有机质积累会抑制土壤碳矿化速率。同时,雪被减少和雪被去除引起土壤降温和含水量降低会抑制土壤氮矿化速率。雪被减少导致土壤氮矿化速率受土壤酶活性降低和有机质积累的影响而降低;雪被去除对土壤有机层中反硝化酶的抑制作用和对土壤总氮的促进作用会降低土壤氮矿化速率,对土壤矿质层中反硝化酶的促进作用和土壤总氮的抑制作用会促进土壤氮矿化速率。综上所述,季节性雪被变化驱动的土壤微环境变化调控土壤温度和含水量动态作用于微生物活性(β-葡聚糖苷酶、纤维素酶、反硝化酶活性和微生物生物量氮)和微生物群落丰富度(真菌和细菌的Chao指数和ACE指数)以及土壤有机质周转,进而影响土壤碳氮矿化过程。相较于自然雪被覆盖下的土壤,雪被减少会抑制土壤碳矿化速率,但对氮矿化速率的影响取决于雪被深度。由雪被减少变化至完全去除雪被,土壤氮矿化速率会从降低转变为增加。这些结果的发现为深入认识亚高山森林生态系统对气候变化的响应与适应机制提供了数据参考。更多还原

【Abstract】 Seasonal snow cover is a crucial ecological factor that controls winter ecological processes in cold ecosystems.However,due to climate warming,the seasonal snow cover in the northern hemisphere has significantly decreased,leading to significant impacts on the seasonal snow cover traits(e.g.snow cover depth,snow cover cycles,and coverage area)of cold ecosystems.Subalpine forest ecosystems in western Sichuan,located on the eastern edge of the Tibetan Plateau,are ecologically sensitive areas that respond to climate change.The reduction of winter snow cover may significantly impact soil microbial biochemical properties and the processes of carbon and nitrogen mineralization by altering the soil microenvironment.However,the mechanisms and effects of these changes have not received adequate attention to date.Therefore,field snow cover manipulation devices were set up in the subalpine Abies faxoniana coniferous forest in western Sichuan,and three treatments were designed: ambient snow cover(control),snow cover removal by 50%(snow reduction treatment),and snow cover removal by 100%(snow removal treatment).The in-situ soil core cultivation method was employed to study the effects of seasonal snow variations on soil micro-environment,microbial activity,microbial biomass,microbial community composition and diversity,and soil carbon and nitrogen mineralization rate in the soil organic and mineral layer of Abies faxoniana forest during key periods of winter(snow formation,coverage,and melt periods)and growth season(early-,middle-,and late growth season)from 2018 to 2020.The main results are as follows:(1)The highest depth of winter snow cover was measured at 39 ± 4 cm.In the snow reduction and snow removal treatments,the depth decreased by 53.63% and 100% compared to the control,respectively.The snow cover treatments(snow reduction and snow removal)caused more severe fluctuations in soil temperature.The mean temperature of the soil organic layer decreased by 0.41°C and 0.24°C,and that of the soil mineral layer decreased by 0.58°C and 0.47°C,respectively,due to the snow reduction and snow removal.The effect of snow reduction on soil temperature in winter was the most significant,whereas snow removal resulted in lower soil temperature in the growth season.As a result of the snow reduction and removal,the frequency of soil freeze-thaw cycles increased by 17.67 and15.33 times,and soil water content decreased by 1.34% and 13.13%,respectively.However,the snow cover treatments did not significantly affect soil p H.(2)The effect of snow cover treatments on soil β-glucosidase activity was only significant,but its interaction with the sampling season had a significant impact on soil β-glucosidase,cellulase,urease,and nitrate reductase activities,with significant differences observed between various soil layers.Snow reduction and snow removal decreased β-glucosidase activity by 5.23%～11.61% and urease activity by 8.35%～10.77%,but increased nitrate reductase activity in the soil organic layer by 7.58%～11.80% and decreased it in the soil mineral layer by 3.56%～9.88%,respectively.In winter,snow reduction and snow removal inhibited the activities of β-glucosidase,cellulase,and nitrate reductase,but promoted urease activity in the soil organic layer during the snow formation period.In the late growth season,snow reduction and snow removal inhibited urease activity and significantly promoted nitrate reductase activity.Although the snow cover treatments had minimal impact on soil microbial biomass carbon content,they significantly increased microbial biomass nitrogen content by 39.18%～79.18%.The snow formation and melt periods were when microbial biomass nitrogen increased the most.(3)In comparison to the control,snow reduction and removal significantly increased the Chao and ACE abundance indices for fungi and bacteria,with increases of 3.13～6.41%and 6.41%～2.54% for fungi,and 2.12～5.95% and 2.00%～5.92% for bacteria.Winter was primarily when there were significant microbial abundance changes.Snow reduction increased the abundance of Basidiomycota fungi and Acidobacteria bacteria at the phylum level while decreasing the abundance of Mortierellomycota fungi and Actinobacteria bacteria.At the genus level,snow reduction led to an increase in the Boletaceae fungi and a decrease in the Mortierella,Acidothermus and Acidimicrobiia bacteria.The fungal and bacterial communities were not signigicantly changed by the snow removal treatment,though.(4)The snow cover treatments had a significant impact on the soil carbon mineralization rate,but snow reduction and snow removal had opposite effects on the soil nitrogen mineralization rate.Snow reduction and snow removal reduced the soil carbon mineralization rate by 11.39% ～ 26.14% compared to the control.However,snow reduction lowered the soil nitrogen mineralization rate by 122.50%,snow removal increased it by178.39%.Additionally,the concentrations of soil organic matter,total nitrogen,dissolved organic carbon,and dissolved organic nitrogen were significantly impacted by the snow cover treatments.Soil organic matter concentration increased by 30.72% ～ 121.6% as a result of snow reduction and snow removal,and dissolved organic nitrogen concentration increased by 42.54% ～ 132.09%.Snow reduction and snow removal led to a 32.85% increase in the concentration of dissolved organic carbon in the soil organic layer and an 11.42%decrease in the soil mineral layer.Snow reduction and snow removal caused a 63.06%increase in the total nitrogen concentration in the soil organic layer,and both treatments led to an equivalent increase and decrease of 9.68% in the soil mineral layer.(5)The partial least square structural equation modeling(PLS-SEM)showed that,the snow reduction and snow removal suppressed the soil carbon mineralization rate through soil cooling,decreased enzyme activity,and soil organic matter accumulation.Simultaneously,soil nitrogen mineralization rates were lowered by soil cooling and decreased water content driven on by snow reduction and snow removal.The soil nitrogen mineralization rate is decreased by lowered soil enzyme activity and organic matter accumulation due to snow reduction.Inhibitory effects of snow removal on denitrifying enzymes and promoting effects on total nitrogen decrease the soil nitrogen mineralization rate in the soil organic layer,and promoting effects of snow removal on denitrifying enzymes and inhibiting effects on total nitrogen increase the soil nitrogen mineralization rate in the soil mineral layer.In conclusion,the soil micro-environment variations driven by seasonal snow reduction and removal can affect soil carbon and nitrogen mineralization by regulating soil temperature and water content dynamics to alter microbial activity(β-glucosidase,cellulase,denitrifying enzyme activity and microbial biomass nitrogen),microbial community richness(Chao and ACE indices for fungi and bacteria),soil organic matter turnover.In comparison to soil with an ambient snow cover,snow reduction diminised the of soil carbon mineralization rate.However,the effect on the soil nitrogen mineralization rate depends on the snow cover depth.From the reduction of snow cover to the complete removal of snow cover,the soil nitrogen mineralization rate will change from decreasing to increasing.These results offer reference data to shed insight on how subalpine forest communities are responding to and adapting to climate change.更多还原