Effects of Experimental Warming and Canada Goldenrod Invasion on the Diversity and Function of the Soil Nematode Community

Both global warming and alien plant invasion can affect the biotic communities in the soil. Most studies are focused on the soil microbial community, but little is known about how global warming, along with alien plant invasion, affects the diversity and function of the soil nematode community. In this study, the individual and interactive effects of experimental warming and Canada goldenrod (Solidago canadensis L.) invasion on soil nematode communities were measured. Experimental air warming, in combination with different levels of S. canadensis invasion, were applied. The results showed that S. canadensis invasion significantly increased chao1, maturity, and structure indexes of the nematode community by 31.44%, 25.57%, and 329.3%, respectively, and decreased the basal index by 48.70% (all p < 0.05). Only the Simpson index was affected by the interaction between warming and S. canadensis invasion. Warming enhanced the S. canadensis invasion effect on the soil nematode community. The changes in nematode community were correlated with shifts in nutrient availability and resource stoichiometry, as well as microbes in the soil. These findings demonstrated that global warming and S. canadensis invasion may, directly and indirectly, alter the soil nematode community, which may considerably affect the functioning of underground food webs.

Soil <i>δ</i>¹⁵N is a better indicator of ecosystem nitrogen cycling than plant <i>δ</i>¹⁵N: A global meta-analysis

The nitrogen-15 (15N) natural abundance composition (δ15N) in soils or plants is a useful tool to indicate the openness of ecosystem N cycling. This study aimed to evaluate the influence of the experimental warming on soil and plant δ15N. We applied a global meta-analysis method to synthesize 79 and 76 paired observations of soil and plant δ15N from 20 published studies, respectively. Results showed that the mean effect sizes of the soil and plant δ15N under experimental warming were −0.524 (95 % CI (confidence interval): −0.987 to −0.162) and 0.189 (95 % CI: −0.210 to 0.569), respectively. This indicated that soil δ15N had negative response to warming at the global scale, where warming had no significant effect on plant δ15N. Experimental warming significantly (p<0.05) decreased soil δ15N in Alkali and medium-textured soils, in grassland/meadow, under air warming, for a 4–10-year warming period and for an increase of >3 ∘C in temperature, whereas it significantly (p<0.05) increased soil δ15N in neutral and fine-textured soils and for an increase of 1.5–3 ∘C in temperature. Plant δ15N significantly (p<0.05) increased with increasing temperature in neutral and fine-textured soils and significantly (p<0.05) decreased in alkali soil. Latitude did not affect the warming effects on both soil and plant δ15N. However, the warming effect on soil δ15N was positively controlled by the mean annual temperature, which is related to the fact that the higher temperature can strengthen the activity of soil microbes. The effect of warming on plant δ15N had weaker relationships with environmental variables compared with that on soil δ15N. This implied that soil δ15N was more effective than plant δ15N in indicating the openness of global ecosystem N cycling.

Seasonal Acclimation Modulates the Impacts of Simulated Warming and Light Reduction on Temperate Seagrass Productivity and Biochemical Composition

Increases in seawater temperature and reduction in light quality have emerged as some of the most important threats to marine coastal communities including seagrass ecosystems. Temperate seagrasses, including Zostera marina, typically have pronounced seasonal cycles which modulate seagrass growth, physiology and reproductive effort. These marked temporal patterns can affect experimental seagrass responses to climate change effects depending on the seasons of the year in which the experiments are conducted. This study aimed at evaluating how seasonal acclimatization modulates productivity and biochemical responses of Zostera marina to experimental warming and irradiance reduction. Seagrass shoots were exposed to different temperatures (6, 12, 16, 20, and 24°C), combined with high (180 μmol photons m–2 s–1) and low (60 μmol photons m–2 s–1) light conditions across four seasons (spring: April, summer: July, and autumn: November 2015, and winter: January 2016). Plants exhibited similar temperature growth rates between 16 and 20°C; at 24°C, a drastic reduction in growth was observed; this was more accentuated in colder months and under low irradiance conditions. Higher leaf growth rates occurred in winter while the largest rhizomes were reached in experiments conducted in spring and summer. Increases in temperature induced a significant reduction in polyunsaturated fatty acids (PUFA), particularly omega-3 (n-3 PUFA). Our results highlight that temperate seagrass populations currently living under temperature limitation will be favored by future increases in sea surface temperature in terms of leaf and rhizome productivity. Together with results from this study on Z. marina from a temperate region, a wider review of the reported impacts of experimental warming indicates the likely reduction in some compounds of nutritional importance for higher trophic levels in seagrass leaves. Our results further demonstrate that data derived from laboratory-based studies investigating environmental stress on seagrass growth and acclimation, and their subsequent interpretation, are strongly influenced by seasonality and in situ conditions that precede any experimental exposure.