Flowering Strategies
The unpredictable and very small amounts of rain (from 26 to 169 mm/year in the centre part of the Negev Desert) occur in winter (Evenari et al. 1982; Evenari 1985). Not only the amount of rain, but also the dates and amounts of the one to three rain even
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Flowering Strategies
2.1
Introduction
The unpredictable and very small amounts of rain (from 26 to 169 mm/year in the centre part of the Negev Desert) occur in winter (Evenari et al. 1982; Evenari 1985). Not only the amount of rain, but also the dates and amounts of the one to three rain events that may engender germination of annual plants are unpredictable. However, during most of the last 25 years, the largest rainfall of the season with rains occurred in December or January and the month with the maximum amount of rain was January (Evenari and Gutterman 1976; Gutterman 1993, 1998a, 1999, 2001a) (Fig. 1.7; Tables 1.2, 1.3). The young seedlings may emerge in the season with rain and mild temperatures (Fig. 1.4),when the days are shortening, from November to 21 December, or when they are lengthening, from 21 December to February or March, or even at the beginning of April (Evenari and Gutterman 1966;Gutterman 1999) (Fig.2.1). In the Saharo-Arabian phytogeographic region, which includes the Negev Desert of Israel, summer begins between mid April and May (Figs. 1.17,1.19;Tables 1.4,1.6), with high temperatures and evaporation rates, very low daytime RH and lengthening days (Gutterman 1999) (Figs. 1.3-1.5). In such an environment, when the beginning of the growing season is unpredictable, but the beginning of the dry and hot season is more predictable, different plant species occurring in the Negev and other similar deserts have developed many adaptations and strategies of flowering. These comprise a portion of the sets of complementary adaptation and survival strategies that have developed in desert plants (Gutterman 1998a, 2000a,b,) (Tables 1.1, 2.1, 2.2). The adaptations and strategies of the flowering process of plant species occurring in deserts enable them, or at least increase their Y. Gutterman, Survival Strategies of Annual Desert Plants © Springer-Verlag Berlin Heidelberg 2002
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Flowering Strategies
Oct Nov Dec Jan
Feb Mar Api May Jun
Jul
Aug Sep Oct
Nov Dec
~ 15
@14
I::
~ 13
10
Strategy Plant Year Schi. 1962
0
G
~--------~o
v
e-~--------- 0
F.L.D .
1963 1964 1965 Carr. 1961 1964
D.I .F.
1)00--- 0------ . 0
G
V
0----
0----
F S 0------0
0------- ......... 0
Sals. 1961
S.H.T.
B
O""- ......... -- -- - ~o _____ 0 ..... _0
v
1964
1965 i i i
i i i
Oct Nov Dec Jan
i i i
Feb Mar Api May Jun
i i i
Jul
i i i
Aug Sep Oct
Nov Dec
MONTH Fig. 2.1. A Day length in Jerusalem on 21st of each month, from sunrise to sunset (solid line). Photoperiodic day length (from morning light intensity of 51x to the same intensity in the evening; dashed line). B Date of germination (G), length ofvegetative period (V), first appearance of flowers (F) and seed maturation (S), of Schismusarabicus(Schi.) (F.L.D.) Carrichtera annua (Carr.) (D.I.F.) and Salsola inermis (Sals.) (S.H.T.), as observed in a natural area near Avdat in various years. (Evenari and Gutterman 1966).
Table 2.1. Number of leaves at flower bud appearance, age (days ± SE) at first flower opening, plant death, and at flower
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