植被综合生态质量时空变化动态监测评价模型

为了能掌握全国植被综合生态质量的高低及其时空变化,构建了既能反映植被生产力又能反映植被覆盖度的植被综合生态质量指数,建立了植被综合生态质量指数年际对比和多年变化趋势评价模型。利用构建的指数和评价模型,以2017年作为监测评价的当年,以2000—2017年作为评价的多年时段,对全国植被综合生态质量时空变化进行了监测评价。结果表明：（1）2017年全国大部地区植被综合生态质量指数高于2000—2016年多年平均值,生态质量偏好;2017年福建、广西、海南、广东、云南植被综合生态质量位居全国前五位,构建的植被综合生态质量指数及其年际对比模型可以定量反映全国植被综合生态质量的空间差异和年际差异。（2）全国有90.7%的区域2000—2017年植被综合生态质量指数呈提高趋势,东北地区西部、内蒙古东部、华北大部、西北地区东部、西南地区东部、华南西部等地生态质量指数提升明显,构建的植被综合生态质量指数多年变化趋势评价模型可以定量反映植被生态质量的多年变化趋势和幅度。（3）南方大部地区2000—2017年平均年植被综合生态质量指数在50.0以上,北方大部地区在50.0以下;我国中东部大部地区在20.0以上,西部大部地区在20.0以下,表明南方大部地区年植被生态质量好于北方、中东大部好于西部。可见,构建的植被综合生态质量指数及其年际对比和多年变化趋势评价模型,能够监测评价当年和多年全国植被综合生态质量的时空变化,可为掌握全国植被生态质量动态提供模型和方法。     

北部湾涠洲岛水域发现上颌和须板异常的布氏鲸:对保护的启示

2018年初以来,北部湾涠洲岛附近出现了布氏鲸（Balaenoptera edeni）的活动。一头上颌与须板异常的小布氏鲸个体引发热议,其视频在网络上广泛流传。我们在船只调查时,目击该个体10次,其以单独活动为主（90%）,主要出现在涠洲岛到斜阳岛之间的水域,最小凸多边形家域面积为14km2,核心家域面积为166.9km²。然而,在 2019年3月30日我们发现该个体已死亡漂浮在海面,根据尸体腐烂状况来推测,该个体的死亡时间大约为3~5日,死亡原因不明。根据照片和现场解剖分析,推测该小布氏鲸的上颌和鲸须异常可能是被渔网或绳索缠绕导致的。由于无法从外形上确认属于哪一个亚种,因此我们测定了该个体的线粒体DNA D-loop（mitochondrial DNA, mtDNA）和细胞色素b（cytochrome b, Cyt b）基因,分别得到909bp和395bp的序列,经比对和系统发育重建,发现该个体属于近岸分布的小布氏鲸亚种（Eden’s whale, B. e. edeni）。由于小布氏鲸具有一定季节迁移特性,我们无法判断造成其上颌伤害的渔网或绳索是否在中国水域。尽管如此,仍然建议当地部门应加强宣传,减少渔网等海洋垃圾的丢弃和排放,为小布氏鲸营造一个安全的栖息环境。     

Effects of Different Potassium (K) Fertilizer Rates on Yield Formation and Lodging of Rice

As one of the most important nutrients for plants, potassium (K) has substantial effects on growth and development of crops. Present study was conducted in three different sites in South China in late season in 2019 with the objective to study the effects of different applied amounts of K fertilizer on yield formation and lodging of rice. Four K fertilizer treatments, K₀: 0 kg potassium oxide (K₂O) ha⁻¹ (control); K₁: 64.20 kg K₂O ha⁻¹ ; K₂: 128.55 kg K₂O ha⁻¹ and K₃ 153.90 kg K₂O ha⁻¹ were applied in the field experiment. The results showed that K₂ and K₃ treatments significantly increased panicle number per unit area, grain number per panicle, seed-setting rate and the grain yield of rice compared with K₀ treatment. Higher net photosynthetic rates were recorded in K₂ and K₃ treatments than K₀ treatment at tillering stage, heading stage and maturity stage. K fertilizer treatments also increased the chlorophyll content and dry matter accumulation by 6.16–23.52% and 21.32–64.59% compared with K₀ treatment, respectively. Moreover, the total N and K accumulation in the aboveground tissues of rice significantly increased under K₂ and K₃ treatments compared with K₀ treatment. Furthermore, compared with K₀ treatment, K fertilizer treatments significantly enhanced the breaking-resistant strength by 40.94–144.24% and reduced the lodging index of rice by 13.14–36.72%.     

秦巴山地NPP及对气候变化响应的多维地带性与暖温带-亚热带界线

秦巴山地位于我国的南北过渡带,对我国生态地理格局产生重要影响。为了探索秦巴山地植被净第一性生产力(NPP,Net Primary Productivity)的时空格局及其气候响应的多样性和复杂性,为我国暖温带-亚热带界线的具体分布提供新的佐证,基于2000—2015年的MOD17A3的地表植被NPP数据和秦巴山地93个气象站点数据,从经度、纬度、海拔、坡向多个维度研究了秦巴山地地表植被NPP的分布及与气候因子的关系。结果表明:从2000—2015年,(1)秦巴山地中低山地区,自北向南随纬度降低,地表植被多年平均NPP呈现增加的趋势,体现了纬度地带性;年均NPP与温度的关系由负相关变为正相关,转折点出现在汉江;与降水的相关性减弱。(2)自西向东多年平均NPP值先增加后减少,秦岭一线地表植被年均NPP与温度由正相关变为负相关,与降水主要呈正相关,相关性先增加后减少。(3)随高度的增加,秦巴山地多年NPP值及增长率均呈现先增加后减少的趋势。(4)秦岭和大巴山多年平均NPP均呈现增加趋势,但是秦岭增长较大巴山更明显;2000m以下,秦岭南坡增长率明显高于北坡,大巴山北坡增长率明显高于南坡;2000—3000m,秦岭南北坡差异较小,但是大巴山差异明显;中山地区(1000—2500m),秦岭年均NPP与气温呈负相关,而大巴山则呈现正相关或弱相关;秦岭地区年均NPP与降水的相关性整体强于大巴山地区。这就意味着全球变暖、气温升高对秦岭植被尤其是中低山地区的植被产生不利影响,但是对大巴山则有利,而前者植被生长主要与降水增加有关。这也说明了基于汉江为界的秦岭和大巴山无论是地表植被NPP的均值还是其南北坡差异以及对气候因子的响应呈现了明显的差异,而汉江作为中山地区植被NPP与气温相关性由正相关性到负相关的转折点,与降水的关系由弱相关到正相关的转折点,更合适作为南北分界线。     

Precipitation regime controls bryosphere carbon cycling similarly across contrasting ecosystems

In arctic and boreal ecosystems, ground bryophytes play an important role in regulating carbon (C) exchange between vast belowground C stores and the atmosphere. Climate is changing particularly fast in these high-latitude regions, but it is unclear how altered precipitation regimes will affect C dynamics in the bryosphere (i.e. the ground moss layer including senesced moss, litter and associated biota) and the closely associated upper humus layer, and how these effects will vary across contrasting environmental conditions. Here, we set up a greenhouse experiment in which mesocosms were assembled containing samples of the bryosphere, dominated by the feather moss Hylocomium splendens, and the upper humus layer, that were collected from across a boreal forest chronosequence in northern Sweden which varies strongly in nutrient availability, productivity and soil biota. We tested the effect of variation in precipitation volume and frequency on CO₂ exchange and dissolved organic carbon (DOC) export, and on moss growth. As expected, reduced precipitation volume and frequency lowered net CO₂ efflux, DOC export and moss growth. However, by regulating moisture, the lower bryosphere and humus layers often mediated how precipitation volume and frequency interacted to drive C dynamics. For example, less frequent precipitation reduced moss growth only when precipitation volume was low. When volume was high, high moisture content of the humus layer helped avoid moss desiccation. Variation in precipitation regime affected C cycling consistently in samples collected across the chronosequence, despite large environmental variation along the sequence. This suggests that the bryosphere exerts a strong buffering effect on environmental variation at the forest floor, which leads to similar responses of C cycling to external perturbations across highly contrasting ecosystems. As such, our study indicates that projected increases in droughts and ground evapotranspiration in high-latitude regions resulting from climate change will consistently reduce C losses from moss-dominated ecosystems.     

降水变化与氮添加对晋北盐碱化草地土壤净氮矿化的影响

于2018年在晋北典型农牧交错带盐碱化草地设置增减降水和氮添加处理试验, 2019年生长季(5—9月)采用原位顶盖PVC埋管法测定不同水、氮处理下土壤净氮矿化速率,研究盐碱化草地土壤净氮矿化速率对降水格局变化和氮沉降的响应。结果表明: 土壤净氮矿化速率表现出明显的季节动态。单独增减降水(±50%)和氮添加(10 g·m^-2·a^-1)以及氮添加+增加50%降水处理对土壤净氮矿化速率影响不显著,氮添加+减少50%降水处理显著提高土壤净硝化速率和净氮矿化速率,分别提高10.8和8.6倍。土壤净氮矿化速率与土壤含水量呈显著正相关,与土壤pH值呈显著负相关。氮添加在不同降水条件下对晋北盐碱化草地土壤氮矿化速率的影响存在差异,土壤含水量与pH值是晋北盐碱化草地土壤净氮矿化速率的主要影响因素。因此,全面评估草地土壤氮矿化过程对全球变化的响应模式,需要考虑降水格局变化与氮沉降增加的交互作用,以及盐碱化草地土壤理化性质的特殊性。     

亚热带6个典型树种吸收细根寿命与形态属性格局

根周转是地下生态过程的主要驱动力, 根属性指征了物种生态策略, 根寿命与属性是理解生态系统碳氮循环和群落多样性的关键。目前对亚热带常绿阔叶林根周转等生态过程的直接观测资料缺乏。该研究对中亚热带江西樟树试验林场6个树种吸收细根动态进行了2年观测, 获取了2.8万张微根管照片, 分析了吸收细根寿命年际和季节变化特征及其与根形态属性的关系。结果显示: 1)亚热带6个树种间吸收细根寿命变异为4.6倍, 变异系数可达73%。中值寿命排序为: 红豆杉(Taxus wallichiana)(426天) >复羽叶栾树( Koelreuteria bipinnata)(155天) >竹柏( Nageia nagi)(145天) >樟( Cinnamomum camphora)(126天) >东京樱花( Cerasus yedoensis)(93天) >深山含笑( Michelia maudiae)(92天); 2)树木吸收细根寿命年际、季节变异较大, 可能是适应伏秋旱、雨热不同期、年际变化大的亚热带季风气候的结果; 3)吸收细根寿命与直径呈显著正相关关系, 与比根长呈显著负相关关系, 表明根的构建成本可以在一定程度上预测寿命。这些结果为预测亚热带地下生态过程、揭示亚热带常绿阔叶林碳氮循环、物种共存机制提供依据。     

A large proportion of North American net ecosystem production is offset by emissions from harvested products,river/stream evasion,and biomass burning

Diagnostic carbon cycle models produce estimates of net ecosystem production (NEP, the balance of net primary production and heterotrophic respiration) by integrating information from (i) satellite‐based observations of land surface vegetation characteristics; (ii) distributed meteorological data; and (iii) eddy covariance flux tower observations of net ecosystem exchange (NEE) (used in model parameterization). However, a full bottom‐up accounting of NEE (the vertical carbon flux) that is suitable for integration with atmosphere‐based inversion modeling also includes emissions from decomposition/respiration of harvested forest and agricultural products, CO₂ evasion from streams and rivers, and biomass burning. Here, we produce a daily time step NEE for North America for the year 2004 that includes NEP as well as the additional emissions. This NEE product was run in the forward mode through the CarbonTracker inversion setup to evaluate its consistency with CO₂ concentration observations. The year 2004 was climatologically favorable for NEP over North America and the continental total was estimated at 1730 ± 370 TgC yr^?1 (a carbon sink). Harvested product emissions (316 ± 80 TgC yr^?1), river/stream evasion (158 ± 50 TgC yr^?1), and fire emissions (142 ± 45 TgC yr^?1) counteracted a large proportion (35%) of the NEP sink. Geographic areas with strong carbon sinks included Midwest US croplands, and forested regions of the Northeast, Southeast, and Pacific Northwest. The forward mode run with CarbonTracker produced good agreement between observed and simulated wintertime CO₂ concentrations aggregated over eight measurement sites around North America, but overestimates of summertime concentrations that suggested an underestimation of summertime carbon uptake. As terrestrial NEP is the dominant offset to fossil fuel emission over North America, a good understanding of its spatial and temporal variation – as well as the fate of the carbon it sequesters ─ is needed for a comprehensive view of the carbon cycle.     

Bryophyte‐cyanobacteria associations as regulators of the northern latitude carbon balance in response to global change

Ecosystems in the far north, including arctic and boreal biomes, are a globally significant pool of carbon (C). Global change is proposed to influence both C uptake and release in these ecosystems, thereby potentially affecting whether they act as C sources or sinks. Bryophytes (i.e., mosses) serve a variety of key functions in these systems, including their association with nitrogen (N₂)‐fixing cyanobacteria, as thermal insulators of the soil, and producers of recalcitrant litter, which have implications for both net primary productivity (NPP) and heterotrophic respiration. While ground‐cover bryophytes typically make up a small proportion of the total biomass in northern systems, their combined physical structure and N₂‐fixing capabilities facilitate a disproportionally large impact on key processes that control ecosystem C and N cycles. As such, the response of bryophyte‐cyanobacteria associations to global change may influence whether and how ecosystem C balances are influenced by global change. Here, we review what is known about their occurrence and N₂‐fixing activity, and how bryophyte systems will respond to several key global change factors. We explore the implications these responses may have in determining how global change influences C balances in high northern latitudes.     

Net primary productivity and rain‐use efficiency as affected by warming,altered precipitation,and clipping in a mixed‐grass prairie

Grassland productivity in response to climate change and land use is a global concern. In order to explore the effects of climate change and land use on net primary productivity (NPP), NPP partitioning [f_BNPP, defined as the fraction of belowground NPP (BNPP) to NPP], and rain‐use efficiency (RUE) of NPP, we conducted a field experiment with warming (+3 °C), altered precipitation (double and half), and annual clipping in a mixed‐grass prairie in Oklahoma, USA since July, 2009. Across the years, warming significantly increased BNPP, f_BNPP, and RUE_BNPP by an average of 11.6%, 2.8%, and 6.6%, respectively. This indicates that BNPP was more sensitive to warming than aboveground NPP (ANPP) since warming did not change ANPP and RUE_ANPP much. Double precipitation stimulated ANPP, BNPP, and NPP but suppressed RUE_ANPP, RUE_BNPP, and RUE_NPP while half precipitation decreased ANPP, BNPP, and NPP but increased RUE_ANPP, RUE_BNPP, and RUE_NPP. Clipping interacted with altered precipitation in impacting RUE_ANPP, RUE_BNPP, and RUE_NPP, suggesting land use could confound the effects of precipitation changes on ecosystem processes. Soil moisture was found to be a main factor in regulating variation in ANPP, BNPP, and NPP while soil temperature was the dominant factor influencing f_BNPP. These findings suggest that BNPP is critical point to future research. Additionally, results from single‐factor manipulative experiments should be treated with caution due to the non‐additive interactive effects of warming with altered precipitation and land use (clipping).