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Modelling temperature effects on plant residue toxicity

M. An1, I. R. Johnson2 and J. V. Lovett2

1Environmental and Analytical Laboratories, Charles Sturt University, Wagga Wagga, NSW 2678, Australia.
2
Department of Agronomy and Soil Science, University of New England, Armidale, NSW 2351, Australia

Abstract

A mechanistic model of residue allelopathy was modified to include a temperature function to simulate effects of temperature on allelochemical production. Different temperature regimes do not alter the pattern of residue allelopathy, i.e. at the early stage of decomposition allelochemical production reaches its maximum, and declines as decomposition proceeds, but modify its intensity and extent. As temperature increases, peak allelochemical production increases while the persistence of allelochemical production decreases.

Key words

residue allelopathy, allelochemical(s), mathematical modelling, plant residue

Introduction

Decomposition of plant residues releases secondary metabolites that exhibit phytotoxic effects on other plants (2).The potential phytotoxicity is dependent on numerous factors, such as residue type, temperature, moisture, aeration, soil texture, inorganic ions, decomposition time, and residue placement, etc., that together govern the rate of residue decomposition, the net rate of active allelochemical production and the subsequent degrees of phytotoxicity. Among these factors, temperature has the great effect on the rate of active phytotoxic compound production from decomposing residue in soil. A mechanistic model of residue allelopathy that was constructed before (1) only simulates allelopathic phenomena caused by decaying plant residues. The present modelling work develops this residue model by considering the temperature factor, examines the residue phytotoxicity under different temperatures, and further increases our understanding of this phenomenon.

Description of the model

The model developed before (1) consists of two parts,

ie. (1)

and

(2)

where

amount of allelochemicals produced (g) at time t
P
biological response to allelochemicals, expressed as % control
t
decomposition time, day
R
amount of plant residue (g) at time t
rate constants of allelochemical release & degradation, day –1
……... parameters

In this paper the effect of temperature () on the production of allelochemicals by residues is expressed through the effects on k1 and k2. The Q10 equation, widely used in ecological models, is used to define :

, ,

where T is temperature (C), and Tr is a reference temperature, taken to be 20C in the model.

Results and discussion

Figure 1 shows a generalised simulation of residue allelopathy under two temperature regimes, 10C, and 30C. At high temperature, plant residues decompose rapidly and allelochemical release/decomposition is accelerated. Soon after decomposition starts, a high concentration of allelochemicals could build up in the soil environment. Consequently, the growth of test plants is severely inhibited. The dissipation of allelochemicals and consumption of substrate are both accelerated as temperature increases, which results in rapid decrease in net rate of allelochemical accumulation, and its short persistence. As decomposition continues growth is stimulated by the low concentration of allelochemicals, and then returns to control level. At low temperature, the situation is reversed. Plant residues decompose slowly, it takes a longer time than at high temperature for allelochemicals to build up, and peak production is significantly lower than that at high temperature. Consequently, the maximum inhibition due to phytotoxicity is not as severe as at high temperature. However, because of low consumption of substrate residue and low degradation rate of allelochemicals, plant residues retain the potential to produce allelochemicals longer.

Figure 1. Effect of different temperature regimes on (a) allelochemical production, and (b) residue phytotoxicity.

Generally speaking, peak allelochemical production increases with increasing temperature and the persistence of allelochemical production decreases with increasing temperature. Even though different temperature regimes result in various peak concentrations of allelochemicals and persistence of production, the pattern of residue allelopathy is not changed, i.e. at the early stage of decomposition allelochemical production reaches its maximum, and declines as decomposition proceeds. Different temperature only modifies its intensity and extent. This is consistent with the literature (3).

References

(1) An, M., Johnson, I. and Lovett, J. 1996 Allelopathy J. 3, 33-42.

(2) Kohli, R.K., Singh, H.P. and Batish, D.R. (eds.) 2001 “Allelopathy in Agroecosystems.” Food Produts Press, New York, 447pp.

(3) Toai, T.V. and Linscott, D.L. 1979 Weed Sci. 27, 595-598.

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