XIV
Contents
18.2 Species Distribution Gradients in the Desert ......... 361
18.3 Variation in Moisture and Temperature
as Selective Forces for Photosynthetic Variation ...... 363
18.3.1 Predictability of Precipitation. . . . . . . . . . . . . . . . . . . . .. 364
18.3.2 Drought Duration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 368
18.3.3 Predictability of Temperature ...................... 369
18.4 Gas Exchange Patterns Among Life-Forms .......... 370
18.4.1 Photosynthetic Pathway Distribution
Among Life-Forms.... . . . .... . . . .... . . .... .... ... 370
18.4.2 Environment and Life-Form Distribution. . . . . . . . . . .. 374
18.5 Longevity and Gas Exchange ...................... 377
18.5.1 Water Use in Relation to Carbon Gain ............. 377
18.5.2 Gas Exchange Flux Versus Set Point. . . . . . . . . . . . . . .. 377
18.5.3 Carbon Isotope Discrimination as a Measure
of Intercellular Carbon Dioxide Concentration ....... 379
18.5.4 Intercellular CO 2 and Life History in C 3 Plants ...... 380
18.6 Integrating Gas Exchange Across Complex
Environmental Gradients. . . . . . . . . . . . . . . . . . . . . . . . .. 382
18.6.1 Evaporative Gradients ............................ 382
18.6.2 Utilization of Summer Moisture Inputs ............. 384
18.7 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 387
References ...................................... 387
19
Deuterium Content in Organic Material of Hosts
and Their Parasites ............................... 393
H. Ziegler
19.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 393
19.2 The Relative Deuterium Content in the Host
and Parasitic Organic Material in Different Kinds
of Parasite Performance .......................... 394
19.2.1 Isotope Contents of Galls ......................... 394
19.2.2 Isotope Contents of Holoparasites
and Their Host Plants ............................ 395
19.2.3 Isotope Contents of Mistletoes (Hemiparasites)
and Their Hosts ................................. 399
19.3 What Are the Reasons
for the Isotope Discriminations? ................... 405
19.3.1 013C ............................................ 405
19.3.2 oD ............................................. 406
19.4 Conclusions... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 407
References ...................................... 408
20
Photosynthesis of Vascular Plants:
Assessing Canopy Photosynthesis by Means
of Simulation Models ............................ 409
W. Beyschlag, R. J. Ryel, and M. M. Caldwell