How Does Nitrogen Application Rate Affect Plant Functional Traits and Crop Growth Rate of Perennial Ryegrass-Dominated Permanent Pastures?

High doses of nitrogen (N) fertiliser input on permanent pastures are crucial in terms of N surplus and N losses. Quantitative analyses of the response of plant functional traits (PFT) driving crop growth rate (CGR) under low N input are lacking in frequently defoliated pastures. This study aimed to understand the significance of PFTs for productivity and N uptake in permanent grasslands by measuring dynamics in tiller density (TD), tiller weight (TW), leaf weight ratio (LWR), leaf area index (LAI), specific leaf area (SLA), as well as leaf N content per unit mass (LNCm) and per unit area (LNCa) in perennial ryegrass (Lolium perenne)-dominated pastures, in a simulated rotational grazing approach over two consecutive growing seasons. Annual N application rates were 0, 140 and 280 kg N ha−1. The phenological development of perennial ryegrass was the main driver of CGR, N uptake and most PFTs. The effect of N application rate on PFTs varied during the season. N application rate showed the greatest effect on TD, LAI and, to a lesser extent, on SLA and LNCm. The results of this study highlight the importance of TD and its role in driving CGR and N uptake in frequently defoliated permanent pastures.

Repeated patterns in the evolution of size in island plants

<p>For reasons not fully understood, animals often evolve predictably on islands. For example, radiations of large, flightless birds are a common element of many island biotas. However, our understanding of how plants evolve on islands is comparatively poor. Further, an investigation into the evolution of island plants could help resolve unanswered questions about island animals. This thesis investigates insular size changes in a range of plant functional traits. First (Chapter 2), I explored size changes in 9 species of vines that have colonized islands from the New Zealand and Australian mainland. I asked whether leaf–stem allometry prohibits leaves and stems from evolving independently from one another. Island populations consistently produced larger leaves than did mainland populations. Moreover, changes in leaf size were not associated with concomitant changes in stem size, suggesting that trait allometry does not govern trait evolution on islands. Next (Chapter 3), I asked whether plants obey the infamous island rule, a putative trend in island evolution wherein small animals become large on islands and large animals become small. I demonstrate that plant stature and leaf area obey the island rule, and seed size does not. My findings illustrate that the island rule is more pervasive than previously considered, but that support for its predictions vary among plant functional traits. Third (Chapter 4), I demonstrate that the island rule results from evolutionary drift along bounded trait domains. The island rule has long been hypothesized to result from a suite of selective pressures. Applying my model to island plants, I show that evolutionary drift is the most parsimonious explanation for the island rule pattern. Finally (Chapter 5), to explore insular patterns in leaf size evolution, I conducted a large-scale, macroevolutionary analysis of leaf size on 98 of New Zealand’s offshore islands. Leaf gigantism was emblematic of island populations, and was most prominent in taxa with variable leaf morphologies on the mainland. Further, leaf gigantism was greatest in populations inhabiting old, distant islands, suggesting that time since divergence is a direct predictor of morphological differentiation between mainland and island populations. Overall, this thesis reveals novel patterns, and helps disentangle the distinct roles of natural selection and drift, in the evolution of plant form and function on islands. Finally, this thesis illustrates how investigating the changes in plant traits can help identify the evolutionary mechanisms operating on islands.</p>

Repeated patterns in the evolution of size in island plants

<p>For reasons not fully understood, animals often evolve predictably on islands. For example, radiations of large, flightless birds are a common element of many island biotas. However, our understanding of how plants evolve on islands is comparatively poor. Further, an investigation into the evolution of island plants could help resolve unanswered questions about island animals. This thesis investigates insular size changes in a range of plant functional traits. First (Chapter 2), I explored size changes in 9 species of vines that have colonized islands from the New Zealand and Australian mainland. I asked whether leaf–stem allometry prohibits leaves and stems from evolving independently from one another. Island populations consistently produced larger leaves than did mainland populations. Moreover, changes in leaf size were not associated with concomitant changes in stem size, suggesting that trait allometry does not govern trait evolution on islands. Next (Chapter 3), I asked whether plants obey the infamous island rule, a putative trend in island evolution wherein small animals become large on islands and large animals become small. I demonstrate that plant stature and leaf area obey the island rule, and seed size does not. My findings illustrate that the island rule is more pervasive than previously considered, but that support for its predictions vary among plant functional traits. Third (Chapter 4), I demonstrate that the island rule results from evolutionary drift along bounded trait domains. The island rule has long been hypothesized to result from a suite of selective pressures. Applying my model to island plants, I show that evolutionary drift is the most parsimonious explanation for the island rule pattern. Finally (Chapter 5), to explore insular patterns in leaf size evolution, I conducted a large-scale, macroevolutionary analysis of leaf size on 98 of New Zealand’s offshore islands. Leaf gigantism was emblematic of island populations, and was most prominent in taxa with variable leaf morphologies on the mainland. Further, leaf gigantism was greatest in populations inhabiting old, distant islands, suggesting that time since divergence is a direct predictor of morphological differentiation between mainland and island populations. Overall, this thesis reveals novel patterns, and helps disentangle the distinct roles of natural selection and drift, in the evolution of plant form and function on islands. Finally, this thesis illustrates how investigating the changes in plant traits can help identify the evolutionary mechanisms operating on islands.</p>

Physiological Responses of Robinia pseudoacacia and Quercus acutissima Seedlings to Repeated Drought-Rewatering Under Different Planting Methods

Changing precipitation patterns have aggravated the existing uneven water distribution, leading to the alternation of drought and rewatering. Based on this variation, we studied species, namely, Robinia pseudoacacia and Quercus acutissima, with different root forms and water regulation strategy to determine physiological responses to repeated drought-rewatering under different planting methods. Growth, physiological, and hydraulic traits were measured using pure and mixed planting seedlings that were subjected to drought, repeated drought-rewatering (i.e., treatments), and well-irrigated seedlings (i.e., control). Drought had negative effects on plant functional traits, such as significantly decreased xylem water potential (Ψmd), net photosynthetic rate (AP), and then height and basal diameter growth were slowed down, while plant species could form stress imprint and adopt compensatory mechanism after repeated drought-rewatering. Mixed planting of the two tree species prolonged the desiccation time during drought, slowed down Ψmd and AP decreasing, and after rewatering, plant functional traits could recover faster than pure planting. Our results demonstrate that repeated drought-rewatering could make plant species form stress imprint and adopt compensatory mechanism, while mixed planting could weaken the inhibition of drought and finally improve the overall drought resistance; this mechanism may provide a theoretical basis for afforestation and vegetation restoration in the warm temperate zone under rising uneven spatiotemporal water distribution.

Competition and Plant Trait Plasticity of Invasive (Wedelia trilobata) and Native Species (Wedelia chinensis, WC) under Nitrogen Enrichment and Flooding Condition

Nitrogen (N) is the important nutrition that regulatory plant functioning and environmental stability of invasive plant species under flooding (F) conditions. Little information clarifies the role of nitrogen enrichment and flooding on the invasive plant functional traits and competition with native competitors. Plant functional traits play an essential role in the successful growth of plants under different environmental conditions. Therefore, greenhouse pots experiment was conducted with invasive plant species (Wedelia trilobata, WT), and its native competitor (Wedelia chinensis, WC) in monoculture and cocultivation culture, along with flooding and nitrogen enrichment conditions. Considering the impact of flooding (F) and nitrogen (N) on an individual basis, the plant physiological traits of WC were nonsignificant compared to that of WT. However, in the combination of flooding × additional nitrogen (F.N, F.2N), plant physiological traits of WT were comparatively higher than those of WC, especially in cocultivation. In flooding × additional nitrogen (F.N and F.2N), better phenotypic plasticity at different plant traits makes WT more dominant in resource competition over WC. In conclusion, improved functional traits of WT under nitrogen enrichment and flooding conditions enhanced its competitiveness over native competitors.

The Role of Woody Plant Functional Traits for Sustainable Soil Management in the Agroforestry System of Ethiopia

A woody plant functional trait that directly affects its fitness and environment is decisive to ensure the success of an Agroforestry practice. Hence, recognizing the woody plant functional traits is very important to boost and sustain the productivity of the system when different plants are sharing common resources, like in Agroforestry system. Therefore, the objective of this paper was to understand how woody plant functional traits contribute to sustainable soil management in Agroforestry system and to give the way forward in the case of Ethiopia. The contribution of woody plant species in improving soil fertility and controlling soil erosion is attributed by litter accumulation rate and the season, decomposability and nutrient content of the litter, root physical and chemical trait, and spread canopy structure functional trait. However, spread canopy structure functional trait is used in coffee based Agroforestry system, while with management in Parkland Agro forestry System. Woody species of Agroforestry system added a significant amount of soil TN, OC, Av.P, K, Na, Ca, and Mg nutrients to the soil. Woody plant species of Agroforestry system and their functional traits are very important to ensure sustainable soil management. Thus, further investigation of the woody plant functional traits especially the compatibility of trees with cops is needed to fully utilize the potential of woody species for sustainable soil management practice.