Rb. Jackson et Mm. Caldwell, INTEGRATING RESOURCE HETEROGENEITY AND PLANT PLASTICITY - MODELING NITRATE AND PHOSPHATE-UPTAKE IN A PATCHY SOIL ENVIRONMENT, Journal of Ecology, 84(6), 1996, pp. 891-903
1 We used the Barber-Cushman model of nutrient uptake to simulate the
importance of soil heterogeneity and root plasticity for nitrate (NO3-
) and phosphate (P) uptake. Model inputs included root physiological p
arameters and soil characteristics obtained from five years of field s
tudies in the sagebrush steppe. At an intensively sampled field site t
he average variation in soil P and NO; around individual plants was 3-
fold and 12-fold (3 x and 12 x, respectively), the range of soil varia
bility used in our simulations. 2 In soil patches three-fold enriched
in P (3 x), simulated P uptake was three to four times greater than in
soil of background P concentrations (1 x). The importance of soil het
erogeneity and root plasticity was even more pronounced for NO3-. In 1
2 x soil patches, NO3- uptake was 7-20 times greater than at 1 x, depe
nding on simulation conditions. Plasticity (root proliferation and inc
reased uptake kinetics) accounted for up to 75% of NO3- and over 50% o
f P acquired from enriched soil patches. Even without plasticity, nutr
ient uptake increased substantially in enriched patches because of hig
her soil-solution concentrations. 3 Using the same model we simulated
P and NO3- uptake for an actual 0.25-m(2) soil area in the field. Plan
t acquisition of P in this area was 28% higher with root plasticity th
an without, equally attributable to root proliferation and increased u
ptake kinetics. Plant NO3- uptake was 61 % greater with plasticity, du
e almost exclusively to increased uptake capacity of roots. 4 We also
simulated P and NO3- uptake in hypothetical soil arrays containing an
equivalent quantity of nutrient distributed homogeneously or heterogen
eously. A plant without plasticity always acquired less P or NO3- in t
he heterogeneous arrays than in the homogeneous arrays. With plasticit
y, it acquired more nutrients in three of four cases compared to the h
omogeneous 'control'. 5 We present these simulations as a way to integ
rate field experiments, generate and test hypotheses, and stimulate di
scussion. Given that heterogeneity is the norm rather than the extreme
, our simulations highlight the importance of soil heterogeneity and r
oot plasticity for both nutrient acquisition and plant competition in
the field.