Trade-offs and synergies between ecosystem productivity and stability in temperate grasslands

Aim

It is crucial to monitor how the productivity of grasslands varies with its temporal stability for management of these ecosystems. However, identifying the direction of the productivity–stability relationship remains challenging because ecological stability has multiple components that can display neutral, positive or negative covariations. Furthermore, evidence suggests that the direction of the productivity–stability relationship depends on the biotic interactions and abiotic conditions that underlie ecosystem productivity and stability. We decipher the relationships between grassland productivity and two components of its stability in four habitat types with contrasting environments and flora.

Location

France.

Time period

2000–2020.

Major taxa

Grassland plant species.

Methods

We used c. 20,000 vegetation plots spread across French permanent grasslands and remotely sensed vegetation indices to quantify grassland productivity and temporal stability. We decomposed stability into constancy (i.e., temporal invariability) and resistance (i.e., maximum deviation from average) and deciphered the direct and indirect effects of abiotic (namely growing season length and nitrogen input) and biotic (namely plant taxonomic diversity, trait diversity and community-weighted mean traits) factors on productivity–stability relationships using structural equation models.

Results

We found a positive relationship between productivity and constancy and a negative relationship between productivity and resistance in all habitats. Abiotic factors had stronger effects on productivity and stability compared with biotic factors. A longer growing season enhanced grassland productivity and constancy. Nitrogen input had positive and negative effects on grassland productivity and resistance, respectively. Trait values affected the constancy and resistance of grassland more than taxonomic and trait diversity, with effects varying from one habitat to another. Productivity was not related to any biotic factor.

Main conclusions

Our findings reveal how vital it is to consider both the multiple components of stability and the interaction between environment and biodiversity to gain an understanding of the relationships between productivity and stability in real-world ecosystems, which is a crucial step for sustainable grassland management.     

Dietary Lysine Imbalance Affects Muscle Proteome in Zebrafish (Danio rerio): A Comparative 2D-DIGE Study

Lysine (Lys) is an indispensable amino acid (AA) and generally the first limiting AA in vegetable protein sources in fish feeds. Inadequate dietary Lys availability may limit protein synthesis, accretion and growth of fish. This experiment aimed to further elucidate the role of Lys imbalance on growth by examining the myotomal muscle proteome of juvenile zebrafish (Danio rerio). Quadruplicate groups of 8 fish were fed either a low-Lys [Lys(-), 1.34?g?kg(-1)], medium/control (Lys, 2.47?g?kg(-1)) or high-Lys [Lys(+), 4.63?g?kg(-1)] diet. Fish growth was monitored from 33 to 49?days post-fertilization (dpf) and trunk myotomal muscle proteome of Lys(-) and Lys(+) treatments were screened by 2D-DIGE and MALDI ToF tandem mass spectrometry. Growth rate was negatively affected by diet Lys(-). Out of 527?±?11 (mean?±?S.E.M.) protein spots detected (～10-150?kDa and 4-7 pI value), 30 were over-expressed and 22 under-expressed in Lys(-) fish (|fold-change| >1.2, p value <0.05). Higher myosin light chains abundance and other myofibrillar proteins in Lys(-) fish pointed to increased sarcomeric degradation, indicating a higher protein turnover for supplying basal energy-saving metabolism rather than growth and muscle protein accretion. The Lys deficiency also possibly induced a higher feeding activity, reflected in the over-expression of beta enolase and mitochondrial ATP synthase. Contrarily, in the faster growing fish [Lys(+)], over-expression of apolipoprotein A-I, F-actin capping protein and Pdlim7 point to increased energy storage as fat and enhanced muscle growth, particularly by mosaic hyperplasia. Thus using an exploratory approach, this study pinpoints interesting candidates for further elucidating the role of dietary Lys on growth of juvenile fish.     

Abiotic constraints and biotic resistance control the establishment success and abundance of invasive <Emphasis Type="Italic">Humulus japonicus</Emphasis> in riparian habitats

Dispersal, abiotic and biotic constraints are all involved in explaining the success of invasive plants but how these factors influence the different life stages of an invader remains poorly known. Focusing on highly invaded riparian habitats we asked: (1) how do propagule pressure, resource availability and resident vegetation influence the success of the invasive Asian vine Humulus japonicus at different stages of its life cycle (i.e. seedling, vegetative and flowering) (2) what is the influence of increasing resource availability on the performance and trait plasticity of H. japonicus compared to a functionally similar co-occurring native species? To answer the first question we performed a repeated field survey along the Gardon River (S France) with detailed measurements of distance to the riverbed, soil characteristics, light availability, and resident vegetation cover. To answer the second question we used a greenhouse experiment to compare the biomass and three functional traits of H. japonicus and Galium aparine along a gradient of increasing water and nitrogen availability. Initial germination success was only determined by abiotic constraints, while the role of biotic resistance increased for later stages with establishment success favoured by the interaction of low resident vegetation cover and high soil fertility, and final integrated success favoured by high light availability. H. japonicus performed better and showed higher plasticity in plant height than G. aparine under increased resource availability while their biomass did not differ in the lower part of the resource gradient. Our study demonstrates that by combining field and experimental studies and analysing responses at different life stages we can gain a more complete understanding of how ecological filters shape successful invasions in the course of the life cycle.     

Effect of long-term treatment with platelet-activating factor on IL-1 and IL-2 production by rat spleen cells

To study the effect of the in vivo administration of platelet-activating factor (PAF) on cytokine production, alzet minipumps loaded with the mediator or solvent alone were connected to the jugular vein and placed under the skin of Sprague-Dawley rats. Over 7 days the animals received total doses of 0.5, 1, 4.5, 9, or 28 micrograms PAF or the solvent alone. The spleen mononuclear cells isolated from Ficoll gradients and the adherent cell fraction were separated before determination of basal and mitogen-stimulated IL-1 and IL-2 production, respectively. Adherent splenocytes from rats having received 28 micrograms PAF exhibited a decreased capability to produce IL-1, as compared to those from vehicle-treated animals. In contrast, adherent splenocytes from rats having received 9 and 4.5 micrograms PAF yielded higher amounts of released and cell-associated IL-1 activity upon LPS stimulation, as compared to those from solvent-treated animals. The PAF antagonist, BN 52021, given orally (5 mg/kg, twice a day throughout the experiments) inhibited the in vivo effect of 28 micrograms PAF. Statistically significant 144 +/- 43% (p less than 0.001, n = 5) and 73 +/- 33%, (p less than 0.01, n = 3) increases in IL-2 production were observed when whole spleen mononuclear cells from rats administered with 1 and 4.5 micrograms PAF, respectively, were stimulated with Con A. BN 52021 markedly inhibited the in vivo effect of 1 microgram PAF on the IL-2 release. Our study demonstrates that PAF can modulate immune functions in vivo and suggests that the specific PAF antagonist, BN 52021, may be used as an immunomodulatory agent.     

Patch dynamics and temporal dispersal partly shape annual plant communities in ephemeral habitat patches

Most organisms in ephemeral habitat patches have resting stages which form a local species pool in response to temporal variations in the patch's availability and suitability. Temporal dispersal from the local species pool may, therefore, be an important process shaping the community assembly, particularly soon after patch creation, and possibly interacting with environmental filtering. As the temporal variation of the environmental conditions has a major effect on the composition of the local species pool, we investigated how well contemporary conditions (both patch availability and patch suitability) and temporal dispersal (approximated by environmental temporal variation and temporal distance) explain the changes in community composition in a given locality through successive ephemeral habitat cycles. We used arable weeds in annual crops as models. We calculated temporal weed community dissimilarity indices between weed communities surveyed in cropping seasons at intervals of two to eight years within a given field. The weeds were surveyed twice each cropping season to account for any changes in the relative contributions of temporal dispersal and contemporary conditions during the season. Patch availability explained most of the temporal weed dissimilarity, suggesting that patch dynamics have the greatest effect on weed community assembly. Temporal distance and temporal variation of the environmental conditions had more effect at the start of the cropping season than later, while patch suitability had more effect in the middle of the season. These results suggest that temporal dispersal drives the weed community assembly when ephemeral habitat patches are created. These assemblies are further shaped by environmental filtering. This is consistent with a temporal source sink dynamic mechanism where the seed bank acts as the main weed source. However, a large part of temporal weed dissimilarity remains unexplained, suggesting that other ecological processes such as spatial dispersal and founder effect may also shape the weed community.     

Mutations in the TGFβ binding-protein-like domain 5 of FBN1 are responsible for acromicric and geleophysic dysplasias

Geleophysic (GD) and acromicric dysplasia (AD) belong to the acromelic dysplasia group and are both characterized by severe short stature, short extremities, and stiff joints. Although AD has an unknown molecular basis, we have previously identified ADAMTSL2 mutations in a subset of GD patients. After exome sequencing in GD and AD cases, we selected fibrillin 1 (FBN1) as a candidate gene, even though mutations in this gene have been described in Marfan syndrome, which is characterized by tall stature and arachnodactyly. We identified 16 heterozygous FBN1 mutations that are all located in exons 41 and 42 and encode TGFβ-binding protein-like domain 5 (TB5) of FBN1 in 29 GD and AD cases. Microfibrillar network disorganization and enhanced TGFβ signaling were consistent features in GD and AD fibroblasts. Importantly, a direct interaction between ADAMTSL2 and FBN1 was demonstrated, suggesting a disruption of this interaction as the underlying mechanism of GD and AD phenotypes. Although enhanced TGFβ signaling caused by FBN1 mutations can trigger either Marfan syndrome or GD and AD, our findings support the fact that TB5 mutations in FBN1 are responsible for short stature phenotypes.     

Generation and characterization of mice with null mutation of the chloride intracellular channel 1 gene

CLIC1 belongs to a family of highly conserved and widely expressed intracellular chloride ion channel proteins existing in both soluble and membrane integrated forms. To study the physiological and biological role of CLIC1 in vivo, we undertook conditional gene targeting to engineer Clic1 gene knock‐out mice. This represents creation of the first gene knock‐out of a vertebrate CLIC protein family member. We first generated a Clic1 Knock‐in (Clic1^FN) allele, followed by Clic1 knock‐out (Clic1^−/−) mice by crossing Clic1^FN allele with TNAP‐cre mice, resulting in germline gene deletion through Cre‐mediated recombination. Mice heterozygous or homozygous for these alleles are viable and fertile and appear normal. However, Clic1^−/− mice show a mild platelet dysfunction characterized by prolonged bleeding times and decreased platelet activation in response to adenosine diphosphate stimulation linked to P2Y₁₂ receptor signaling. genesis 48:127–136, 2010. © 2010 Wiley‐Liss, Inc.