2.3 Measurements of plant flowering phenology
We selected six dominant and common plant species for phenological
observation, including three perennial C3 grasses,S. breviflora , C. ammannii and A. tenuissimum , one
perennial C3 subshrub A. frigida , one
C4 grass, C. songorica , and one perennial
C4 subshrub, K. prostrata. Five individuals per
plant species were randomly chosen and numbered in each plot, and their
reproductive phenology was observed and recorded using the measured
scoring method. Here, the phenological observation of a species started
once the first flower buds were discovered. The observation frequency
was once every 3 to 5 days. For grasses and non-grasses, a 6-point
system (Dunne et al., 2003) and a 4-point system (Price & Waser, 1998)
were used to record scores, respectively. The phenological phases
observed were 0 = spikelet in boot, 1 = spikelet out of boot, 2 =
exserted anthers and styles, 3 = developing seed, 4 = all seed
dropped (Price & Waser, 1998).
For non-grass plants, plant phenology can be divided into seven stages:
0, not flowering; 1. flower buds appear. 2. flowering. 3. flower
senescence. 4. the fruit begins to develop. 5. the fruit begins to
disperse. 6. The fruit falls off completely. Each phenological event was
recorded as the corresponding day of year. The actual phenological
sequences of plants were then used to fit Richard’s equation in 1STOPT
software (Sherry et al., 2007). The date and duration of each
phenological period were calculated based on the optimal simulation
curve according to the Richards equation (Price & Waser, 1998).
Y = K/ (1 + a*exp(-b*X)) m
where ”K” is the maximum growth, that is, the maximum value in the
phenology score; ”a” is the start-up parameter of the date when
observation of the evaluated species began; ”b” is the reproductive
phenological rate during the observed period; and ”m” is the curve shape
variation parameter. All phenological scores were well described by the
Richards equation (R2 > 0.99).
Four parameters can be determined by equation fitting and substituted
into the conversion formula as follows.