Evaluation and Performance of the APSIM Crop Growth Model for German Winter Wheat, Maize and Fieldpea Varieties in Monocropping and Intercropping Systems

Competition for solar radiation between plants grown in multi-species cropping systems can severely limit crop production of individual species within that system. There are various approaches for modeling light interception within mixed-cropping and row or strip intercropping systems. To extend the knowledge about model behavior and different model approaches under interspecific competition conditions, the Agricultural Production Systems Simulator （APSIM） was evaluated and calibrated for field experiments previously described and simulated by the Decision Support System for Agrotechnology Transfer （DSSAT）. Initially the APSIM plant model was successfully modified to simulate wheat, maize and fieldpea monocultures in the European agro-ecological zone. Once calibrated, the APSIM model was then used to simulate a strip relay intercropping maize/wheat and maize/fieldpea system. In DSSAT, a shading algorithm was introduced to modify the daily weather input in order to take competition for solar radiation into account. In contrast, APSIM simulates interspecific competition using a modified Beer＇s law for multi-component canopy conditions. After a re-evaluation of the model regarding a minimum change of crop coefficients and variables, APSIM was able to simulate dry matter and grain yield of German maize, wheat and fieldpea varieties adequately. However, APSIM is a point-based model, and many of the processes that influence strip cropping cannot be accommodated by adjusting Beer＇s Law alone. So far none of the tested frameworks successfully modeled strip or relay intercropping. The processes governing growth in the numerous and very diversifying intercropping systems are complex and at this point in time have not been captured in sufficient detail.

The asymmetric relationships of the distribution of conspecific saplings and adults in forest fragments

Aims With the increase of land-use change,habitat fragmentation has become a major factor affecting plant diversity.Generally,when the adult density is high,the survival rate of conspecific saplings may decline and provide more resources and space for other species to maintain a high local species diversity.Therefore,the spatial relationship of conspecific saplings and adults(SRCSA)can regulate plant diversity.However,very few studies have assessed SRCSA within fragmented forests,and we still largely unknown the relationship between SRCSA and species diversity in fragmented landscapes.Methods We calculated the mean strength of SRCSA using the spatial distribution data of saplings and adults with a log-transformed hierarchical offset-power model on 27 islands in a land-bridge island system.The higher strength of SRCSA reflects a more negative relationship between the density of conspecific saplings and adults on an island(i.e.the looser pattern of SRCSA).We tested the relationships among island attributes(i.e.island area,the distance to the mainland—MD,and the distance to the nearest island—ND),SRCSA and species diversity.Important Findings The strength of SRCSA increased with ND.Meanwhile,the species diversity significantly increased with the strength of SRCSA,and island area and the strength of SRCSA independently explained 26%and 6%of variation of species diversity,respectively,and their interactions explained 8%.Shade-intolerant and low-abundant species showed looser patterns of SRCSA.Our study suggests that SRCSA may have the effect of excluding species with a relatively low abundance in isolated island forests,which illustrates the importance of biotic interactions in maintaining plant diversity in fragmented forests.Our results also emphasize that we should consider forest connectivity when testing the conspecific negative density dependence.

Heat sensitivity of eggs attributes to the reduction in Agasicles hygrophila population

Agasicles hygrophila has been introduced worldwide as a control agent for the invasive weed Alternanthera philoxeroides.However,global warming has potential impact on its controlling efficacy.The aim of this research was to explore the primary factors responsible for the greatly reduced A.hygrophila population in hot summers.To imitate the temperature conditions in summers,different developmental stages of hygrophila were treated with high temperatures from 32.5℃ to 45℃ for 1-5 h.Based on the survival rate,the heat tolerance of each developmental stage was ranked from lowest to highest as follows:egg,1st,2nd,3rd instar larva,adult and pupa.Eggs showed the lowest heat tolerance with 37.5℃ as the critical temperature affecting larval hatching.Heat treatment of the A.hygrophila eggs at 37.5℃ for 1 h decreased the hatch rate to 24%.Our results indicated that when compared with the control at 25℃,1 h treatment at 37.5℃ prolonged the duration of the egg stage,shortened the duration of oviposition and total longevity,and changed the reproductive pattern of A.hygrophila.The net reproductive rate,intrinsic rate and finite rate were all significantly reduced.The results suggest that low heat tolerance of the eggs was the major factor responsible for the reduction of A.hygrophila populations,and the key temperature was 37.5°C.Therefore,appropriate measures should be taken to protect eggs in order to maintain the efficacy of A.hygrophila in the biological control of A.philoxeroides in hot summers.