Table_6_How to Restore Invertebrate Diversity of Degraded Heathlands? A Case Study on the Reproductive Performance of the Field Cricket Gryllus campestris (L.).DOCX

BackgroundNitrogen (NOx, NHy) and acidifying (NOx, NHy, SOx) deposition has reduced the biodiversity of European dry heathlands. Restoration efforts such as sod-cutting (removal of vegetation, litter and humus layer) often shifted these systems from N to P limitation and have had limited success in restoring the invertebrate community. Possible reasons for this include the unresolved acidification and a change in food plant stoichiometry. Here, we investigate how liming and P addition change food nutritional quality and their consequences for invertebrate performance.
MethodsWe performed feeding experiments with field crickets (Gryllus campestris), using plant material collected from a full factorial field experiment with liming and P addition. We related female reproduction as measure of individual fitness to elemental ratios of plants fed to the crickets.
ResultsP addition stimulated cricket daily reproduction and shortened their reproductive period, resulting in no difference in total reproduction. Liming greatly reduced both daily and total reproduction and resulted in more females cannibalizing on their male mates. Females that did so could partly offset the liming induced reduction in reproduction, suggesting dietary deficiency. P-addition improved food quality (lower N:P ratios) while liming led to skewed Mn:Mg and Fe:Mg ratios that compare unfavorably to ratios found in terrestrial invertebrates.
ConclusionIncreased plant N:P ratio following sod-cutting constrains the reproductive potential in Gryllus campestris in a non-linear way. Liming reduced nutritional quality, likely by inducing deficiencies in Fe or Mn.
Management ImplicationsHigh-impact restoration management practices such as sod cutting and liming cause new problems for invertebrates rooted in ecological stoichiometry. Since P-addition only partially offsets these negative effects, we instead advocate the use of less intensive N removal management and weaker buffering agents to reduce soil acidification. Furthermore, a reduction in N emission is paramount as it will remove the need for disruptive interventions.

研究背景：氮氧化物（NOₓ）与氨（NHᵧ）沉降，以及兼具酸化作用的NOₓ、NHᵧ、硫氧化物（SOₓ）沉降，已导致欧洲干旱石楠荒原（dry heathlands）的生物多样性下降。诸如草皮移除（sod-cutting，即清除植被、枯落物与腐殖质层）的生态修复措施，常使该生态系统从氮限制转向磷限制，但在恢复无脊椎动物群落（invertebrate community）方面效果有限。其潜在原因包括未得到解决的酸化问题，以及食用植物化学计量比（food plant stoichiometry）的改变。本研究旨在探究施石灰（liming）与磷添加（P addition）如何改变食物的营养品质，及其对无脊椎动物生存表现的影响。
研究方法：本研究以田野蟋蟀（Gryllus campestris）为实验对象，采用源自施石灰与磷添加全因子野外实验所采集的植物材料开展摄食实验（feeding experiments）。以雌性繁殖率作为个体适合度（individual fitness）的衡量指标，将其与饲喂蟋蟀的植物元素比例（elemental ratios）进行关联分析。
研究结果：磷添加可提升蟋蟀的日繁殖量，但缩短了其繁殖周期，最终总繁殖量无显著差异。施石灰则大幅降低了蟋蟀的日繁殖量与总繁殖量，并导致更多雌性个体同类相食雄性配偶。发生此类行为的雌性个体可部分抵消施石灰引发的繁殖能力下降，这暗示其存在膳食营养缺乏（dietary deficiency）问题。磷添加改善了食物营养品质（降低了氮磷比N:P），而施石灰则使锰镁比（Mn:Mg）与铁镁比（Fe:Mg）出现失衡，该失衡状态相较于陆生无脊椎动物（terrestrial invertebrates）的适宜比例并不理想。
研究结论：草皮移除后植物氮磷比升高，会以非线性方式限制田野蟋蟀的繁殖潜能。施石灰会降低食物营养品质，这大概率是由铁或锰的营养缺乏所导致。
管理启示：诸如草皮移除与施石灰这类高影响的修复管理措施，会通过生态化学计量学（ecological stoichiometry）机制为无脊椎动物带来新的生存问题。由于磷添加仅能部分抵消这些负面影响，因此我们主张采用强度更低的氮移除管理手段，以及效力更温和的缓冲剂（buffering agents）来缓解土壤酸化。此外，减少氮排放（N emission）至关重要，因为这将消除对这类破坏性干预措施的需求。