Furthermore, 15N-Glu-feeding experiments indicated that tea plants can absorb exogenously applied amino acids that can then be used for N assimilation. In addition, we demonstrated that CsLHT1 and CsLHT6 are involved in the uptake of amino acids from the soil in the tea plant.It has been suggested that tea plants grown inorganic tea plantations are subjected to N-deficient conditions due to the absence of inorganic fertilizer. Compared with conventional tea, that produced under organic management systems contains higher levels of catechins that are linked to antioxidant effects of tea infusions. However, organic tea contains lower levels of amino acids that are also important compounds in terms of tea quality. The decay of large amounts of pruned tea shoots may contribute significantly to soil amino-acid levels inorganic tea plantations; the decomposition of such organic matter and nutrient recycling depends largely on soil fungi. Interestingly, the long-term application of high amounts of N fertilizer was found to reduce soil fungal diversity in tea plantations. This likely could account for why we observed higher amino-acid contents in the organic tea plantation compared with the conventional tea plantation . This implies a more important role for soil amino acids in tea plant grown inorganic tea plantations.It has been reported that, in addition to inorganic N, amino acids can support tree growth. As a perennial evergreen tree species, the tea plant can also use organic fertilizer. However, the role of soil amino acids in tea plant growth and metabolism has not yet been investigated. In this study, we observed that the tea plant could take up 15N-Glu, and Glu feeding increased the aminoacid contents in the roots . This revealed that tea plants can take up amino acids from the soil for use in the synthesis of other amino acids. In our study, nine amino acids were detected in the soil of an organic tea plantation, and the utilization of exogenous Glu was analyzed in detail. In future studies,hydroponic nft it will be important to test the roles of various mixtures of amino acids for use as fertilizers for the growth and metabolism of the tea plant.

The molecular mechanism underlying the uptake of amino acids from the soil by trees has not been thoroughly studied. In this study, we identified seven CsLHTs that were grouped into two clusters, which was consistent with LHTs in Arabidopsis . CsLHT1 and CsLTH6 in cluster I have amino-acid transport activity , which is also consistent with AtLHT1 and AtLHT6. Moreover, these two genes were highly expressed in the roots and both encode plasma membrane-localized proteins . These findings support the hypothesis that CsLHT1 and CsLHT6 play important roles in amino-acid uptake from the soil . However, the members of cluster II, CsLHT2, CsLHT3, CsLHT4, CsLHT5, and CsLHT7, did not display amino-acid transport activity . Interestingly, except for AtLHT1 and AtLHT6, there are no other AtLHTs being shown to transport amino acids. It is possible that cluster II LHTs are involved in the transport of metabolites other than amino acids. For example, AtLHT2 was recently shown to transport 1-aminocyclopropane-1- carboxylic acid, a bio-synthetic precursor of ethylene, in Arabidopsis.LHT1 has been thoroughly characterized as a high affinity-amino-acid transporter and has a major role in the uptake of amino acids from the soil in both Arabidopsis and rice. In contrast, there is only one report on the function of AtLHT6; it is highly expressed in the roots, and the atlht6 mutant presented reduced aminoacid uptake from media when supplied with a high amount of amino acids. Although the authors did not characterize the amino-acid transport kinetics for AtLHT6, their results are consistent with this protein being a low-affinity-amino-acid transporter. In the present study, we characterized CsLHT1 to be a high-affinity amino-acid transporter , with a capacity to transport a broad spectrum of amino acids . By contrast, CsLHT6 exhibited a much lower affinity for 15N-Glu, and it also displayed higher substrate specificity. Considering that amino-acid concentrations in the soil of tea plantations are low , CsLHT1 may play a more important function than CsLHT6 in the uptake of amino acids from the soil into tea plants. However, in soils, amino-acid contents could be much higher, locally, particularly in the vicinity of decomposing animal or vegetable matter. In this situation, CsLHT6 may play an important role in the uptake of amino acids. In addition,CsLHT6 is also highly expressed in the major veins of mature leaves , suggesting a role for CsLHT6 in amino-acid transport within these tea leaves.

Given that protocols for the efficient production of transgenic tea cultivars are lacking, CsLHT1 and CsLHT6 expression cannot be modulated by either over expression or CRISPR/Cas9 gene editing. However, in China, there is an abundance of tea plant germplasm resources. CsLHT1 and CsLHT6 are potential gene markers for selecting germplasms that can efficiently take up amino acids. Moreover, germplasms with high CsLHT1 or CsLHT6 expression can be used as root stocks for grafting with elite cultivars to improve the ability of these cultivars to take up amino acids from the soil. Alternatively, these germplasms can be utilized through gene introgression. These grafted lines that can efficiently take up amino acids or novel cultivars should be better suited for use inorganic tea plantations than in conventional tea plantations.One of the core goals of sustainability science is understanding how practitioners make decisions about managing social-ecological systems . In the context of sustainable agriculture, an important research objective is quantifying the economic, environmental, and social outcomes of different farm management practices . However, it is equally important to understand how farmers conceptualize the idea of sustainability and translate it into farm management decisions. The innumerable and often vague definitions of sustainable agriculture make this a challenging task, and fuel the debate about linking sustainability knowledge to action. This debate will remain largely academic without empirical analysis of how farmers think about sustainability in real-world management contexts. These questions are not only relevant to agriculture, but also to all social-ecological systems and the knowledge networks that are in place to support decision making. This paper addresses these issues by analyzing farmer “mental models” of sustainable agriculture. Mental models are empirical representations of an individual’s or group’s internally held understanding of their external world . Mental models reflect the cognitive process by which farmer views about sustainable agriculture are translated into farm management decisions and practice adoption. Our mental models were constructed from content coding of farmers’ written definitions of sustainable agriculture, and were analyzed using network methods to understand the relational nature of different concepts making up a mental model.

We test three hypotheses about mental models of sustainable agriculture. First, mental models are hierarchically structured networks, with abstract goals of sustainability more central in the mental model, which are linked to peripheral concrete strategies from which practitioners select to attain the goals. Second, goals are more likely to be universal across geographies, whereas strategies tend to be adapted to the specific context of different social-ecological systems. Third, practitioners who subscribe to central concepts in the mental model will more frequently exhibit sustainability-related behaviors, including participation in extension activities and adoption of sustainable practices. Our mental model data were drawn from farmers in three major American viticultural areas in California: Central Coast, Lodi, and Napa Valley. California viticulture is well suited for studying sustainability. Local extension programs have used the concept of sustainability since the 1990s ,hydroponic channel and farmer participation in sustainability programs is strong . Furthermore, viticulture is geographically entrenched , with viticultural areas established on the basis of their distinct biophysical and social characteristics . Hence, we expect wine grape growers to have well-developed mental models of sustainability, with geographic variation reflecting social-ecological context.or group’s internally held understanding of the external world . Group mental models, which are the focus of this paper, represent the collective knowledge and understanding of a particular domain held by a specific population of individuals. Mental models are an empirical snapshot of the cognitive process that underpins human decision making and behavior. Mental models complement more traditional approaches to understanding environmental behavior by highlighting the interdependent relationships among attitudes, norms, values, and beliefs . For example, the Values-Beliefs-Norms model of environmental behavior hypothesizes a causal chain running from broad ecological values, to beliefs about environmental issues, to more specific behavioral norms. The network approach used here shows how these types of more general and specific concepts are linked together in a hierarchical and associative structure. Mental models have evolved into an important area of research in environmental policy, risk perception, and decision making . A growing number of researchers are using mental models to better understand decision making in the context of social-ecological systems . Two approaches that are especially relevant to this paper are Actors, Resources, Dynamics, and Interactions and Consensus Analysis . The ARDI approach uses participatory research methods to construct a group mental model of the interactions among stakeholders, resources, and ecological processes . The final product is a graphic conceptualization of how the group perceives the social-ecological system, its components, and their place in it, which can be used to inform management strategies. The CA approach relies on similar data-collection techniques to elicit a group mental model that captures stakeholders’ beliefs and values pertaining to how the social-ecological system should be managed and for what purpose . The mental models are then analyzed using quantitative methods to assess agreement among individuals and identify points for consensus. Along with addressing research questions about practitioner knowledge and decision making, both approaches have been used to facilitate multi-stake holder management of social-ecological systems . This paper conceptualizes group mental models as “concept networks” comprised of nodes representing unique concepts and ties representing associations among concepts.The concept network approach is different from ARDI and CA in that network analysis methods are used to analyze the structure of mental models and measure the importance of individual concepts based on their position in the concept network. This approach follows from Carley’s work , which is founded in the theoretical argument that human cognition operates in an associative manner .

When a given concept is presented to the individual, memory is searched for that concept, ties between the concept and associated concepts are activated, and associated concepts are retrieved. The more associations a given concept has, the more likely the concept is to be recalled. Highly connected concepts serve as cognitive entry points for accessing a constellation of associated ideas. We elicited our mental models from written text of farmers’ definitions of sustainable agriculture, and follow Carley in arguing that written language can be taken as a symbolic expression of human knowledge . It is important to note that our mental models deviate from Carley’s in that the associations among concepts are nondirectional and do not represent causality between concepts. Ties in our concept network represent concept co-occurrence, where two concepts occurred together in a single definition of sustainable agriculture. See Methods for more details.Hypothesis 1 is that mental models are hierarchically structured, with abstract concepts constraining the cognitive associations among more concrete concepts. For example, practitioners who define sustainability primarily as environmental responsibility versus economic viability may evaluate the benefits and costs of management practices with different criteria. This perspective is related to models of political belief systems where specific attitudes on public policy issues are predicted by general beliefs about policies and core values . Construal-level theory also suggests that hierarchical belief-systems contain abstract, superordinate goals related to subordinate beliefs about actions needed to achieve them . The hierarchical structure reflects a basic principle of cognitive efficiency in taxonomic categorization , where more abstract concepts provide cognitive shortcuts to retrieve specific linked attributes . The concepts making up mental models of sustainability can be divided into two basic types, each with different levels of abstraction: goals and strategies . Abstract goals are desirable properties, attributes, and characteristics of a sustainable system to be realized. Examples taken from this study include environmental responsibility, economic viability of the farm enterprise, continuation into the future, or soil health and fertility. Strategies are more concrete and include practices or approaches that are thought to contribute to the realization of abstract goals.