Long‐term impacts of manure amendments on carbon and greenhouse gas dynamics of rangelands

Livestock manure is applied to rangelands as an organic fertilizer to stimulate forage production, but the long‐term impacts of this practice on soil carbon (C) and greenhouse gas (GHG) dynamics are poorly known. We collected soil samples from manured and nonmanured fields on commercial dairies and found that manure amendments increased soil C stocks by 19.0 ± 7.3 Mg C ha^?1 and N stocks by 1.94 ± 0.63 Mg N ha^?1 compared to nonmanured fields (0–20 cm depth). Long‐term historical (1700–present) and future (present–2100) impacts of management on soil C and N dynamics, net primary productivity (NPP), and GHG emissions were modeled with DayCent. Modeled total soil C and N stocks increased with the onset of dairying. Nitrous oxide (N₂O) emissions also increased by ~2 kg N₂O‐N ha^?1 yr^?1. These emissions were proportional to total N additions and offset 75–100% of soil C sequestration. All fields were small net methane (CH₄) sinks, averaging ?4.7 ± 1.2 kg CH₄‐C ha^?1 yr^?1. Overall, manured fields were net GHG sinks between 1954 and 2011 (?0.74 ± 0.73 Mg CO₂ e ha^?1 yr^?1, CO₂e are carbon dioxide equivalents), whereas nonmanured fields varied around zero. Future soil C pools stabilized 40–60 years faster in manured fields than nonmanured fields, at which point manured fields were significantly larger sources than nonmanured fields (1.45 ± 0.52 Mg CO₂e ha^?1 yr^?1 and 0.51 ± 0.60 Mg CO₂e ha^?1 yr^?1, respectively). Modeling also revealed a large background loss of soil C from the passive soil pool associated with the shift from perennial to annual grasses, equivalent to 29.4 ± 1.47 Tg CO₂e in California between 1820 and 2011. Manure applications increased NPP and soil C storage, but plant community changes and GHG emissions decreased, and eventually eliminated, the net climate benefit of this practice.     

Separating spatial search and efficiency rates as components of predation risk

Predation risk is an important driver of ecosystems, and local spatial variation in risk can have population-level consequences by affecting multiple components of the predation process. I use resource selection and proportional hazard time-to-event modelling to assess the spatial drivers of two key components of risk—the search rate (i.e. aggregative response) and predation efficiency rate (i.e. functional response)—imposed by wolves (Canis lupus) in a multi-prey system. In my study area, both components of risk increased according to topographic variation, but anthropogenic features affected only the search rate. Predicted models of the cumulative hazard, or risk of a kill, underlying wolf search paths validated well with broad-scale variation in kill rates, suggesting that spatial hazard models provide a means of scaling up from local heterogeneity in predation risk to population-level dynamics in predator–prey systems. Additionally, I estimated an integrated model of relative spatial predation risk as the product of the search and efficiency rates, combining the distinct contributions of spatial heterogeneity to each component of risk.     

杉木人工林土壤微生物群落结构特征

采用氯仿熏蒸法、稀释平板法和磷脂脂肪酸(phospholipid fatty acid,PLFA)方法,分析了常绿阔叶林转变成杉木人工林后土壤微生物种群数量和群落结构的变化特征.结果表明:常绿阔叶林转变为杉木人工林后,林地土壤的微生物生物量碳、可培养细菌和放线菌数降低.杉木人工林地总PLFAs、细菌PLFAs、真菌PLFAs比常绿阔叶林分别降低了49.4％、52.4％和46.6％,革兰氏阳性和阴性细菌PLFAs远低于常绿阔叶林.杉木人工林根际土壤微生物生物量碳、可培养细菌和放线菌数显著高于杉木人工林林地土壤,根际土壤中总PLFAs、细菌PLFAs、革兰氏阳性和阴性细菌PLFAs的含量也高于林地土壤,但真菌PLFAs和细菌PLFAs之比却低于林地土壤.对土壤微生物群落结构进行主成分分析发现,第1主成分和第2主成分共解释了土壤微生物群落结构变异的78.2％.表明常绿阔叶林与杉木人工林土壤的微生物群落结构间存在差异.     

半干旱区土地利用方式变化对生态系统碳储量的影响

土地利用方式变化对生态系统碳储量具有重要影响,评价不同土地利用方式下陆地生态系统的碳获取能力有助于制定生态系统管理策略,对适应和减缓全球气候变化具有重要的意义.本文以科尔沁地区沙质草地、樟子松-山杏疏林草地、杨树防护林带为对象,量化了不同土地利用方式变化对生态系统碳储量及其分配的影响.结果表明,沙质草地转变为樟子松-山杏疏林草地和杨树防护林带后地上部分碳储量分别为以平均0.17和4.45 t·hm~(-2)·a~(-1)的速率增加;沙质草地、樟子松一山杏疏林草地和杨树防护林带的根系碳储量依次为1.382、1.706和18.541 t·hm~(-2),土壤碳储量依次为26.11、25.20和41.36 t·hm~(-2);沙质草地转变为杨树防护林带后根系碳储量和土壤碳储量增加,平均速率分别为1.07和0.95 t·hm~(-2)·a~(-1);3种土地利用方式的有机碳含量/储量在不同层次土壤之间变异程度不同,相对而言疏林草地变异程度最小.总体来看,3种土地利用方式总碳储量依次为杨树防护林带(131.9 t·hm~(-2))、樟子松-山杏疏林草地(30.0 t·hm~(-2))、沙质草地(28.3 t·hm~(-2)).     

Life-history monographs of Japanese plants. 12: Asarum caulescens Maxim. (Aristolochiaceae)

The life-history characteristics of Asarum caulescens Maxim. (Aristolochiaceae) are described here. This typical summer-green perennial of the Aristolochiaceae is a unique woodland element distributed in central Honshu, that is, south of Fukushima Prefecture to Shikoku and Kyushu, Japan. It grows in the somewhat shady understory of temperate montane deciduous broad-leaved or mixed forests associated with conifers, such as Cryptomeria japonica and Abies firma . One of the unique features of A. caulescens is its rhizome structures in combination with aerial shoots, which play an important role in vegetative propagation. The perennation strategy of A. caulescens is exceedingly complex, producing various combinations of linear or branched rhizomes bearing different numbers of leaves. Rhizomes consist of two or three segments, each 5 mm to 5 cm long as a unit, connected linearly, but also occasionally branched. At the tip of the newly formed rhizome segment, a single leaf or a pair of cordate leaves are formed. Exceedingly complex branching patterns of the rhizome segments were also recognized, forming ramets in late June to early July. Vegetative propagation by ramet formation obviously plays a very important role in the maintenance of local populations.     

青海省牧草产量的遥感估算及其时空分布规律

以青海省为例,基于植被指数(NDVI)和地面实测资料建立了不同草地类型的牧草产量遥感估算模型,并利用地面实测资料对模型精度进行了检验。结果表明,所有模型拟合结果良好(R2≥0.67),精度较高,能够对牧草产量进行动态监测;基于建立的牧草产量遥感估算模型,反演了青海省2004年5~8月基于像元尺度的月牧草产量分布图,并对牧草产量的空间分布特征、时间演变规律进行了详细分析。研究表明,青海省牧草产量空间分布主要与草地类型密切相关,同时也与其地貌、土壤和气候特征有关,而牧草产量的年内季节变化则主要与牧草生长及气候变化规律有关。     

Comparison of methods for assessing the impact of different disturbances and nutrient conditions upon functional characteristics of grassland communities

Background and Aims

Predicting the response of plant communities to variation in resources and disturbance is still a challenge, because findings depend on how ecological gradients are characterized and how grassland functional composition is assessed. Focusing on leaf dry matter content (LDMC), the efficacy of different methods for evaluating the best response of plant communities to either environmental or disturbance change is examined.

Methods

Data were collected on 69 grasslands located at four sites in the Pyrenees and Massif Central. N-Ellenberg indices and plant nutrient content (Ni) were compared to assess fertility, and either LDMC (meas) measured or calculated from a trait database for which traits were measured under the same environmental conditions (db). Management regime (MR) was characterized in terms of categories (grazing, cutting) and plant height.

Key Results

LDMCdb was positively correlated to LDMCmeas, but depended significantly on site temperature. N-Ellenberg and Ni were significantly correlated, and there was a significant effect of MR and temperature. LDMC responded to fertility, MR and temperature. Replacing MR by plant height in an REML analysis reduced the uncertainty of the LDMC prediction. LDMC was correlated to plant height at community level, whereas the correlation was weak at species level. Differences in LDMC between plant communities under any of the management regimes were significantly correlated to the standing herbage mass.

Conclusion

The N-Ellenberg index is a better indicator of fertility than Ni which is short-term and environment-dependent. LDMC taken from a database allows plant trait variation due to species abundance (excluding variation due to trait plasticity in response to management) to be captured. So the former is better suited for assessing agricultural services that mainly depend on plant phenology and tissue composition. LDMC responded to defoliation regime in addition to fertility because plant height is roughly correlated with LDMC at plant community level.     

Spiders as potential indicators of elephant‐induced habitat changes in endemic sand forest,Maputaland, South Africa

Elephant impacts on spider assemblages, and the potential use of spiders as indicators of habitat changes was assessed in central Maputaland, South Africa. Three habitats, namely undisturbed sand forest, elephant disturbed sand forest and mixed woodland, were sampled. To ensure a thorough representation of all spider guilds, spiders were collected by tree beating, sweep netting, active searching, leaf litter sifting and pitfall traps. In total, 2808 individual spiders, representing 36 families, 144 determined genera and 251 species were collected. Spider abundance was highest in the undisturbed sand forest (n = 1129, S = 179), followed by elephant disturbed sand forest (n = 1006, S = 165) and mixed woodland (n = 673, S = 171). Assemblages of the two sand forests were more similar than to the mixed woodland assemblage. Active hunting species were indicators of the more open vegetation of elephant disturbed sand forest (six active hunters, no web‐builders) and mixed woodland (ten active hunters, one web‐builder), whereas web‐builders are indicators of the dense, complex vegetation structure of undisturbed sand forest (six web‐builders, three active hunters). Elephant‐induced changes to the vegetation structure in this high diversity, high endemism region result in changes in the composition of spider assemblages, and may need to be mitigated by management intervention.